QCollator silently fails on Windows

QCollator on Windows uses CompareString(Ex). These methods return 0 on error (source). However, QCollator does not check for this return value (source: qcollator_win.cpp:97). Instead, if a flag is not supported, it returns a negative number for any comparison.

Note that a comparator function with this behavior leads std::sort() to go out-of-bounds with iterators and crash the program.

This can be observed when testing an application with WINE, which does not support SORT_DIGITSASNUMBERS flag. WINE correctly implements CompareStringEx according to Microsoft's documentation (source). For historical context, see also this commit.