getMinFrameCount error handling

Convention is for "get" APIs that directly return status_t and indirectly
return a value via a pointer, to return BAD_VALUE if the pointer is NULL.
Also indirectly return 0 for other errors.

Change-Id: I1599f20ecb26e9723f9fb384ffbf911ff3a2ce1c
diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index 9fd78b3..177359b 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -54,6 +54,11 @@
         audio_stream_type_t streamType,
         uint32_t sampleRate)
 {
+    if (frameCount == NULL) return BAD_VALUE;
+
+    // default to 0 in case of error
+    *frameCount = 0;
+
     // FIXME merge with similar code in createTrack_l(), except we're missing
     //       some information here that is available in createTrack_l():
     //          audio_io_handle_t output