Found by UBSan:
qstring.h:1160:44: runtime error: null pointer passed as argument 1, which is declared to never be null
qstring.h:1160:44: runtime error: null pointer passed as argument 2, which is declared to never be null
Fix by avoiding the memcmp() calls if there's a chance that they
might be called with nullptr.
While at it, also implement !=, >, <=, >= in terms of ==, <,
and add a test, because this particular UB was not fingered by
any of the QtCore test cases, but by a Qt3D one.
Change-Id: I413792dcc8431ef14f0c79f26e89a3e9fab69465
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
a54d44298f