Only read some of TNS bitstream data in the case that the TNS filter order is

non-zero as per the specification.

Patch by Alex Converse (alex converse gmail com)
Fixes another issue pertaining to issue632

Originally committed as revision 15303 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/aac.c

@@ -629,6 +629,7 @@ static int decode_tns(AACContext * ac, TemporalNoiseShaping * tns,
                     tns->order[w][filt] = 0;
                     return -1;
                 }
+                if (tns->order[w][filt]) {
                 tns->direction[w][filt] = get_bits1(gb);
                 coef_compress = get_bits1(gb);
                 coef_len = coef_res + 3 - coef_compress;
@@ -639,6 +640,7 @@ static int decode_tns(AACContext * ac, TemporalNoiseShaping * tns,
                 }
             }
         }
+    }
     return 0;
 }