Dear All.
 
I've got abort crash problem when changing state to ready to pause in twice in playbin3.
 
Actually, we have 3 appsrc and video, audio and text are feed separately.
However, one of qtdemux can not recognize invalid text (e.g. This file contains no playable streams) with application/x-3gp.
Then, the last state return for parsebin1 (qtdemux1) has FAILURE.
  
After that, our player tried to set_state (paused) again in order to 3s buffering (prerolling).
However, gstelement could not filter same changing state out by FAILURE (old return) and Playbin3 tried to setup_next_source () and it got GST_STATE_CHANGE_FAILURE with no_next_group and deactivated current group immediately.
 
And g_assert was happened when pad-removed cb (e.g. when playbin3 is unloaded).
g_assert (combine->srcpad == pad);
But, combine->srcpad is already deactivated and unreffed.
 
So, I wanted to add prevent code in order to solve abort crash problem.
 
Please refer GST log with level 6.
 
Thanks.