ofz+valgrind: Conditional jump or move depends on uninitialised value

if, before lcl_UnicodeStrNCpy is called, aSymbol contains embedded
nulls then the aSymbol.getLength() and the mnRangeOpPosInSymbol value
derived from an earlier aSymbol.getLength() include the range after
the embedded null, while lcl_UnicodeStrNCpy stops at the first
embedded null leaving cSymbol with uninitialized value that
are later read from it.

Conditional jump or move depends on uninitialised value(s)
   at 0x23BFBCA0: ScCompiler::IsReference(rtl::OUString const&, rtl::OUString const*) (compiler.cxx:3275)
   by 0x23BFFF4C: ScCompiler::NextNewToken(bool) (compiler.cxx:4248)
   by 0x23C00D20: ScCompiler::CompileString(rtl::OUString const&) (compiler.cxx:4419)
   by 0x23A29FAF: ScFormulaCell::Compile(rtl::OUString const&, bool, formula::FormulaGrammar::Grammar) (formulacell.cxx:1118)
   by 0x23A278B7: ScFormulaCell::ScFormulaCell(ScDocument*, ScAddress const&, rtl::OUString const&, formula::FormulaGrammar::Grammar, ScMatrixMode) (formulacell.cxx:656)
   by 0x23772EC3: ScColumn::ParseString(ScCellValue&, int, short, rtl::OUString const&, formula::FormulaGrammar::AddressConvention, ScSetStringParam const*) (column3.cxx:1729)
   by 0x2377354B: ScColumn::SetString(int, short, rtl::OUString const&, formula::FormulaGrammar::AddressConvention, ScSetStringParam*) (column3.cxx:1851)
   by 0x23AE2B97: ScTable::SetString(short, int, short, rtl::OUString const&, ScSetStringParam*) (table2.cxx:1369)
   by 0x23897045: ScDocument::SetString(short, int, short, rtl::OUString const&, ScSetStringParam*) (document.cxx:3377)
   by 0x1F35F41C: ScEEImport::WriteToDocument(bool, double, SvNumberFormatter*, bool) (eeimpars.cxx:400)
   by 0x1F366F3B: ScFormatFilterPluginImpl::ScImportRTF(SvStream&, rtl::OUString const&, ScDocument*, ScRange&) (rtfimp.cxx:34)

Change-Id: Iefc6be6c3a383bd9b3cdeaa896c07e24e5100dc7
Reviewed-on: https://gerrit.libreoffice.org/44658Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>

sc/source/core/tool/compiler.cxx

@@ -1931,7 +1931,7 @@ void ScCompiler::SetError(FormulaError nError)
 static sal_Unicode* lcl_UnicodeStrNCpy( sal_Unicode* pDst, const sal_Unicode* pSrc, sal_Int32 nMax )
 {
     const sal_Unicode* const pStop = pDst + nMax;
-    while ( *pSrc && pDst < pStop )
+    while ( pDst < pStop )
     {
         *pDst++ = *pSrc++;
     }