decodebin3: fix warnings on drain and on going PLAYING -> READY -> PLAYING
- Drain signals were printing warnings in decodebin3 for non critical functionality
- the main_input group-id was not being cleared when going from PAUSED to READY. This would mean that if you set the uridecodebin to READY and then back to PLAYING, it would cause the decodebin3 to print a warning (e.g. Group id changed (1 -> 2) on input 0x12218d80), even though the old group id at this point was stale.
Edited by Tim-Philipp Müller