Qt: Avoid deprecated QString:count() with no parameters
Qt-6.4 has deprecated QString:count() with no parameters. Stop using it.
Likely push to main/S3_2 already before 3.1.0-beta1 gets released, and keep only S3_1 patch waiting.
Pushed to main & S3_2, S3_1 waiting.
Qt-6.4 has deprecated QString:count() with no parameters. Stop using it.