stagefright-plugins: check if input queue is empty
stagefright-plugins: check if input queue is empty

input queue may be empty when calling decodeAudio.
Add a guard for it.

DOGEDUMP-4184

Change-Id: I261e8d36fb4560fdcc04702b4e09a00c4b10cc47

BrokenROM/external_stagefright-plugins,BrokenROM/external_stagefright-plugins