Automatically autodetect sound system if old one doesn't exist

[DarthGandalf]

5.2.4, linux

1. compile with phonon support
2. use phonon happily
3. compile without phonon support

Actual result:

"null" sound system is selected, and there's no sound

Expected result:

the sound system should be autodetected in this case, which would select "qt", since "phonon" is not available anymore

https://bugs.gentoo.org/934767