aacsbr: silence message for SBR extension "padding".

Some files contain a few additional, all-0 bits.
Check for that case and don't print incorrect "not supported"
message.
Fixes trac issue #836.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/aacsbr.c

@@ -933,7 +933,9 @@ static void read_sbr_extension(AACContext *ac, SpectralBandReplication *sbr,
         }
         break;
     default:
-        av_log_missing_feature(ac->avctx, "Reserved SBR extensions are", 1);
+        // some files contain 0-padding
+        if (bs_extension_id || *num_bits_left > 16 || show_bits(gb, *num_bits_left))
+            av_log_missing_feature(ac->avctx, "Reserved SBR extensions are", 1);
         skip_bits_long(gb, *num_bits_left); // bs_fill_bits
         *num_bits_left = 0;
         break;