Avoid UBSan pointer-overflow

...as seen with recently introduced UITest_writer_tests
UITEST_TEST_NAME=compareDocuments.compareDocuments.test_tdf137855, but where the
unsigned sal_uLong (aka sal_uIntPtr) value is apparently meant to wrap around
and address an element of m_pMemory at a negative index from m_pBDiag:

> sw/source/core/doc/doccomp.cxx:832:13: runtime error: addition of unsigned offset to 0x6250014a90d0 overflowed to 0x6250014a90b8
>  #0 in (anonymous namespace)::Compare::CompareSequence::Compare(unsigned long, unsigned long, unsigned long, unsigned long) at sw/source/core/doc/doccomp.cxx:832:13
>  #1 in (anonymous namespace)::Compare::CompareSequence::CompareSequence((anonymous namespace)::CompareData&, (anonymous namespace)::CompareData&, (anonymous namespace)::Compare::MovedData const&, (anonymous namespace)::Compare::MovedData const&) at sw/source/core/doc/doccomp.cxx:794:5
>  #2 in (anonymous namespace)::Compare::Compare(unsigned long, (anonymous namespace)::CompareData&, (anonymous namespace)::CompareData&) at sw/source/core/doc/doccomp.cxx:605:25
>  #3 in (anonymous namespace)::CompareData::CompareLines((anonymous namespace)::CompareData&) at sw/source/core/doc/doccomp.cxx:440:17
>  #4 in SwDoc::CompareDoc(SwDoc const&) at sw/source/core/doc/doccomp.cxx:1877:13
>  #5 in SwEditShell::CompareDoc(SwDoc const&) at sw/source/core/edit/editsh.cxx:877:34
>  #6 in SwView::InsertMedium(unsigned short, std::unique_ptr<SfxMedium, std::default_delete<SfxMedium> >, short) at sw/source/uibase/uiview/view2.cxx:2377:39
>  #7 in SwView::DialogClosedHdl(sfx2::FileDialogHelper*) at sw/source/uibase/uiview/view2.cxx:2574:26
[...]

Using std::make_signed_t where its canonic type happens to be `long` requires a
workaround for old Clang to avoid a false

> CXXFunctionalCastExpr, suspicious cast from 'sal_uLong' (aka 'unsigned long') to 'std::make_signed_t<decltype(d)>' (aka 'long') [loplugin:toolslong]

warning.

Change-Id: I07413ba06051f75d80832a4772ab1c541805b259
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/105234
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions