don't crash due to earlier short reads

Change-Id: I682a9bf72cbe18999c0c5acc495e813727e0e372
(cherry picked from commit 0030efe0)
Reviewed-on: https://gerrit.libreoffice.org/17909Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>

sw/source/filter/ww8/ww8par2.cxx

@@ -4382,6 +4382,9 @@ void WW8RStyle::ImportOldFormatStyles()
         if (eSti == ww::stiNil)
             continue;
 
+        if (stcp >= aPAPXOffsets.size())
+            continue;
+
         rSI.bValid = true;
 
         if (ww::StandardStiIsCharStyle(eSti) && !aPAPXOffsets[stcp].mnSize)