Disable popping from audio buffer when streaming is activated

Disable popping from audio buffer when streaming is activated

Streaming thread reads content of audio buffer, so when the
streaming thread is joinable, modifying the buffer itself
can invalidate iterators associated with the buffer container,
which might cause an undefined behavior. For this reason,
limiting the maximum size of the buffer by popping from it
should be disabled when streaming thread is joinable.

Change-Id: I7cea5460cda6abdbee770c6b2818861a35f0080b