Zero out return values in audio binder calls

More specifically when handling GET_OUTPUT_FOR_ATTR in IAudioPolicyService.
This prevents leaking a uninitialized `output` across binder if
getOutputForAttr were to encounter errors.

Bug: 23756261
Change-Id: Ibff8a1249a4e8a3c89a33a540dda428b10d6ca82
diff --git a/media/libmedia/IAudioPolicyService.cpp b/media/libmedia/IAudioPolicyService.cpp
index baa5c7d..7e6b9fc 100644
--- a/media/libmedia/IAudioPolicyService.cpp
+++ b/media/libmedia/IAudioPolicyService.cpp
@@ -877,7 +877,7 @@
             if (hasOffloadInfo) {
                 data.read(&offloadInfo, sizeof(audio_offload_info_t));
             }
-            audio_io_handle_t output;
+            audio_io_handle_t output = 0;
             status_t status = getOutputForAttr(hasAttributes ? &attr : NULL,
                     &output, session, &stream, uid,
                     samplingRate, format, channelMask,