HwAudioSource: wrong native handle check

Playing status of audio source is checked using the native handler
not 0.
However, if AudioSystem#startAudioSource fails, the native handler
returned is not 0, but an error code.
In fact AudioPolicyManager sets the PORT to NONE (0) and sets an error
status.
JNI layer transforms the failure status into a native handler returned
to the caller.

Bug: 186088557
Test: make

Signed-off-by: Francois Gaffie <francois.gaffie@renault.com>
Change-Id: Iaa920c073885c2556a93a1b5ae23467fa6ffad4f