[Rendering] Don't propose audio/video settings which the encoders can't accept
@bilboed
Submitted by Edward Hervey Assigned to Edward Hervey @bilboed
Description
Currently the rendering preferences dialog proposes some choices that encoders might no be able to accept.
For ex : 32bit audio with fluwmaenc (only accepts 16bit audio).
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=433380