audio_thread: prevent calling of absent callback
audio_thread: prevent calling of absent callback

Papapashu/freshplayerplugin,grevutiu-gabriel/freshplayerplugin,grevutiu-gabriel/freshplayerplugin,reuben/freshplayerplugin,Papapashu/freshplayerplugin,Papapashu/freshplayerplugin,reuben/freshplayerplugin,reuben/freshplayerplugin