decode_audio3: initialize AVFrame

Same fix and issue as in a25d912dca

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/utils.c

@@ -1344,7 +1344,7 @@ int attribute_align_arg avcodec_decode_audio3(AVCodecContext *avctx, int16_t *sa
                                               int *frame_size_ptr,
                                               AVPacket *avpkt)
 {
-    AVFrame frame;
+    AVFrame frame = {0};
     int ret, got_frame = 0;
 
     if (avctx->get_buffer != avcodec_default_get_buffer) {