If a signal was invalid, the code still called messageSignature(),
which returns a null QByteArray, and passed its constData() to
qWarning("%s"). That probably worked in our implementation, because it
falls back to QString::asprintf(), but it raised eyebrows, so avoid
calling messageSignature() on invalid QMetaMethod.
This changes the warning output, so adjust the test.
Task-number: QTBUG-123544
Change-Id: I41bc6650de091f61354ff91ee45659668f0e0223
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
d2dbe2d7f7