aacdec: free frame buffer if no audio was decoded

If no decoding error was detected, but still no audio was decoded, the
frame needs to be free'ed, or it will leak.

Fixes part of ticket #2095
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/aacdec.c

@@ -2611,6 +2611,8 @@ static int aac_decode_frame_int(AVCodecContext *avctx, void *data,
 
     if (samples)
         ac->frame->nb_samples = samples;
+    else
+        av_frame_unref(ac->frame);
     *got_frame_ptr = !!samples;
 
     if (is_dmono) {