aacsbr: Turnoff in the event of over read.

Aliased compressed AAC bytes are almost certainly not meaningful SBR
data. In the wild this causes harsh artifacts switching HE-AAC streams
that don't have SBR headers aligned with segment boundaries.

Turning off SBR falls back to a default set of upsampling parameters
that can function as a sort of error concealment. This is consistent
with how the decoder handles other sorts of errors.

Bug-Id: 1047
CC: libav-stable@libav.org
Signed-off-by: Sean McGovern <gseanmcg@gmail.com>

libavcodec/aacsbr.c

@@ -1097,6 +1097,7 @@ int ff_decode_sbr_extension(AACContext *ac, SpectralBandReplication *sbr,
     if (bytes_read > cnt) {
         av_log(ac->avctx, AV_LOG_ERROR,
                "Expected to read %d SBR bytes actually read %d.\n", cnt, bytes_read);
+        sbr_turnoff(sbr);
     }
     return cnt;
 }