QLatin1StringView: fix UB in "a"_L1 <> nullptrHEADdev

Found by ubsan: if rhs is nullptr, then we fed a nullptr as the second
argument of memcmp(), which is UB.

Fix by catching an empty rhs before we reach that line.

Amends e52d50a03da29e2dddaee551e4409f28c7ed56f2 (which, despite
pick-to's to the contrary, never made it into 6.2 or 5.15).

Change b977ae371a753a82e1d0bb32c5b62099da663721 fixed this for
UTF-8/UTF-8 comparison from 6.5 on, but 6.4 ad 6.3 remain vulnerable
there, but they're closed, so can't be fixed anymore.

Pick-to: 6.7 6.5
Change-Id: I12fa986aa82a7440a9d53fad19a15e9420233e0b
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

0 files changed, 0 insertions, 0 deletions