pvs-studio: Possible overflow

Change-Id: Ifa213fd6b719683afae9633615f69db894cd9c18
Reviewed-on: https://gerrit.libreoffice.org/62062
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

writerperfect/qa/unit/EPUBExportTest.cxx

@@ -284,7 +284,7 @@ void EPUBExportTest::testMimetype()
     SvMemoryStream aMemoryStream;
     aMemoryStream.WriteStream(aFileStream);
     OString aExpected("application/epub+zip");
-    CPPUNIT_ASSERT(aMemoryStream.GetSize() > static_cast<sal_uInt64>(38 + aExpected.getLength()));
+    CPPUNIT_ASSERT(aMemoryStream.GetSize() > static_cast<sal_uInt64>(aExpected.getLength()) + 38);
 
     OString aActual(static_cast<const char*>(aMemoryStream.GetData()) + 38, aExpected.getLength());
     // This failed: actual data was some garbage, not the uncompressed mime type.