Handle zero nPLCF

...as found by ASan in CppunitTest_sw_filters_test:

> Testing file:///.../sw/qa/core/data/ww6/pass/crash-1.doc:
> ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6020009382b0 at pc 0x2b1dcb5eabac bp 0x7fffe8ccbdb0 sp 0x7fffe8ccbda8
> READ of size 4 at 0x6020009382b0 thread T0
>  WW8PLCF::SeekPos(int) sw/source/filter/ww8/ww8scan.cxx:2219:14
>  WW8PLCF::WW8PLCF(SvStream&, int, int, int, int, int, int) sw/source/filter/ww8/ww8scan.cxx:2080:9
>  WW8PLCFx_Fc_FKP::WW8PLCFx_Fc_FKP(SvStream*, SvStream*, SvStream*, WW8Fib const&, ePLCFT, int) sw/source/filter/ww8/ww8scan.cxx:2883:21
>  WW8PLCFx_Cp_FKP::WW8PLCFx_Cp_FKP(SvStream*, SvStream*, SvStream*, WW8ScannerBase const&, ePLCFT) sw/source/filter/ww8/ww8scan.cxx:3088:7
>  WW8ScannerBase::WW8ScannerBase(SvStream*, SvStream*, SvStream*, WW8Fib*) sw/source/filter/ww8/ww8scan.cxx:1588:20
>  SwWW8ImplReader::CoreLoad(WW8Glossary*, SwPosition const&) sw/source/filter/ww8/ww8par.cxx:5022:20
>  SwWW8ImplReader::LoadThroughDecryption(SwPaM&, WW8Glossary*) sw/source/filter/ww8/ww8par.cxx:5767:19
>  SwWW8ImplReader::LoadDoc(SwPaM&, WW8Glossary*) sw/source/filter/ww8/ww8par.cxx:6039:19
>  WW8Reader::Read(SwDoc&, rtl::OUString const&, SwPaM&, rtl::OUString const&) sw/source/filter/ww8/ww8par.cxx:6157:20
>  SwReader::Read(Reader const&) sw/source/filter/basflt/shellio.cxx:175:18
>  SwDocShell::ConvertFrom(SfxMedium&) sw/source/uibase/app/docsh.cxx:258:22
>  SfxObjectShell::DoLoad(SfxMedium*) sfx2/source/doc/objstor.cxx:790:23
>  SwFiltersTest::filter(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) sw/qa/core/filters-test.cxx:112:20
>  SwFiltersTest::load(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int) sw/qa/core/filters-test.cxx:71:12
>  test::FiltersTest::recursiveScan(test::filterStatus, rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) unotest/source/cpp/filters-test.cxx:129:20
>  test::FiltersTest::testDir(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) unotest/source/cpp/filters-test.cxx:154:5
>  SwFiltersTest::testCVEs() sw/qa/core/filters-test.cxx:154:5
> 0x6020009382b1 is located 0 bytes to the right of 1-byte region [0x6020009382b0,0x6020009382b1)
> allocated by thread T0 here:
>  operator new[](unsigned long) /home/sbergman/clang/trunk/src/projects/compiler-rt/lib/asan/asan_new_delete.cc:64
>  WW8PLCF::ReadPLCF(SvStream&, int, unsigned int) sw/source/filter/ww8/ww8scan.cxx:2091:26
>  WW8PLCF::WW8PLCF(SvStream&, int, int, int, int, int, int) sw/source/filter/ww8/ww8scan.cxx:2075:9
>  WW8PLCFx_Fc_FKP::WW8PLCFx_Fc_FKP(SvStream*, SvStream*, SvStream*, WW8Fib const&, ePLCFT, int) sw/source/filter/ww8/ww8scan.cxx:2883:21
>  WW8PLCFx_Cp_FKP::WW8PLCFx_Cp_FKP(SvStream*, SvStream*, SvStream*, WW8ScannerBase const&, ePLCFT) sw/source/filter/ww8/ww8scan.cxx:3088:7
>  WW8ScannerBase::WW8ScannerBase(SvStream*, SvStream*, SvStream*, WW8Fib*) sw/source/filter/ww8/ww8scan.cxx:1588:20
>  SwWW8ImplReader::CoreLoad(WW8Glossary*, SwPosition const&) sw/source/filter/ww8/ww8par.cxx:5022:20
>  SwWW8ImplReader::LoadThroughDecryption(SwPaM&, WW8Glossary*) sw/source/filter/ww8/ww8par.cxx:5767:19
>  SwWW8ImplReader::LoadDoc(SwPaM&, WW8Glossary*) sw/source/filter/ww8/ww8par.cxx:6039:19
>  WW8Reader::Read(SwDoc&, rtl::OUString const&, SwPaM&, rtl::OUString const&) sw/source/filter/ww8/ww8par.cxx:6157:20
>  SwReader::Read(Reader const&) sw/source/filter/basflt/shellio.cxx:175:18
>  SwDocShell::ConvertFrom(SfxMedium&) sw/source/uibase/app/docsh.cxx:258:22
>  SfxObjectShell::DoLoad(SfxMedium*) sfx2/source/doc/objstor.cxx:790:23
>  SwFiltersTest::filter(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) sw/qa/core/filters-test.cxx:112:20
>  SwFiltersTest::load(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int) sw/qa/core/filters-test.cxx:71:12
>  test::FiltersTest::recursiveScan(test::filterStatus, rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) unotest/source/cpp/filters-test.cxx:129:20
>  test::FiltersTest::testDir(rtl::OUString const&, rtl::OUString const&, rtl::OUString const&, SfxFilterFlags, SotClipboardFormatId, unsigned int, bool) unotest/source/cpp/filters-test.cxx:154:5
>  SwFiltersTest::testCVEs() sw/qa/core/filters-test.cxx:154:5

Change-Id: I97d995aad621b829b6fb6ee4622d386fec0bedea
Reviewed-on: https://gerrit.libreoffice.org/17963Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 1a871f9d)
Reviewed-on: https://gerrit.libreoffice.org/17967Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>

sw/source/filter/ww8/ww8scan.cxx

@@ -2107,7 +2107,8 @@ WW8PLCF::WW8PLCF(SvStream& rSt, WW8_FC nFilePos, sal_Int32 nPLCF, int nStruct,
 void WW8PLCF::ReadPLCF(SvStream& rSt, WW8_FC nFilePos, sal_uInt32 nPLCF)
 {
     sal_Size nOldPos = rSt.Tell();
-    bool bValid = checkSeek(rSt, nFilePos) && (rSt.remainingSize() >= nPLCF);
+    bool bValid = nPLCF != 0 && checkSeek(rSt, nFilePos)
+        && (rSt.remainingSize() >= nPLCF);
 
     if (bValid)
     {