Improve error reporting in AudioTrack JNI

for android_media_AudioTrack_get_min_buff_size when it
calls AudioTrack::getMinFrameCount.  That AudioTrack API
has been changed recently to guarantee that it will always
return a valid frameCount if the return value == NO_ERROR.

Change-Id: I8f7f850f1c30229ce77a02bdc963634cdbaf3aac