...as seen during CppunitTest_vcl_pdfexport:

> workdir/UnpackedTarball/pdfium/core/fxcrt/string_data_template.h:81:31: runtime error: null pointer passed as argument 2, which is declared to never be null
> /usr/include/string.h:44:28: note: nonnull attribute specified here
>     #0 0x7f6506471c0d in fxcrt::StringDataTemplate<char>::CopyContentsAt(unsigned long, char const*, unsigned long) workdir/UnpackedTarball/pdfium/core/fxcrt/string_data_template.h:81:5
>     #1 0x7f650645f9db in fxcrt::ByteString::ByteString(fxcrt::StringViewTemplate<char> const&, fxcrt::StringViewTemplate<char> const&) workdir/UnpackedTarball/pdfium/core/fxcrt/bytestring.cpp:137:12
>     #2 0x7f6505e6bfbc in fxcrt::operator+(char const*, fxcrt::ByteString const&) workdir/UnpackedTarball/pdfium/core/fxcrt/bytestring.h:242:10
>     #3 0x7f650671798c in CFX_FolderFontInfo::ReportFace(fxcrt::ByteString const&, _IO_FILE*, unsigned int, unsigned int) workdir/UnpackedTarball/pdfium/core/fxge/cfx_folderfontinfo.cpp:223:21
>     #4 0x7f6506716ea1 in CFX_FolderFontInfo::ScanFile(fxcrt::ByteString const&) workdir/UnpackedTarball/pdfium/core/fxge/cfx_folderfontinfo.cpp:193:5
>     #5 0x7f65067154fb in CFX_FolderFontInfo::ScanPath(fxcrt::ByteString const&) workdir/UnpackedTarball/pdfium/core/fxge/cfx_folderfontinfo.cpp:151:36
>     #6 0x7f650671546a in CFX_FolderFontInfo::ScanPath(fxcrt::ByteString const&) workdir/UnpackedTarball/pdfium/core/fxge/cfx_folderfontinfo.cpp:151:15
>     #7 0x7f6506714c86 in CFX_FolderFontInfo::EnumFontList(CFX_FontMapper*) workdir/UnpackedTarball/pdfium/core/fxge/cfx_folderfontinfo.cpp:121:5
>     #8 0x7f650676d271 in CFX_FontMapper::LoadInstalledFonts() workdir/UnpackedTarball/pdfium/core/fxge/cfx_fontmapper.cpp:360:16
>     #9 0x7f650676d469 in CFX_FontMapper::MatchInstalledFonts(fxcrt::ByteString const&) workdir/UnpackedTarball/pdfium/core/fxge/cfx_fontmapper.cpp:365:3
>     #10 0x7f6506773376 in CFX_FontMapper::FindSubstFont(fxcrt::ByteString const&, bool, unsigned int, int, int, int, CFX_SubstFont*) workdir/UnpackedTarball/pdfium/core/fxge/cfx_fontmapper.cpp:573:22
[...]

Change-Id: I0221a099198d8f23f239e8493509bdf1816fbc59