avcodec/mlpdec: Do not leave invalid values in matrix_out_ch[] on error

Fixes: runtime error: index 12 out of bounds for type 'uint8_t [8]'
Fixes: 1832/clusterfuzz-testcase-minimized-6574546079449088

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mlpdec.c

@@ -729,8 +729,7 @@ static int read_matrix_params(MLPDecodeContext *m, unsigned int substr, GetBitCo
         av_log(m->avctx, AV_LOG_ERROR,
                "Number of primitive matrices cannot be greater than %d.\n",
                max_primitive_matrices);
-        s->num_primitive_matrices = 0;
-        return AVERROR_INVALIDDATA;
+        goto error;
     }
 
     for (mat = 0; mat < s->num_primitive_matrices; mat++) {
@@ -743,12 +742,12 @@ static int read_matrix_params(MLPDecodeContext *m, unsigned int substr, GetBitCo
             av_log(m->avctx, AV_LOG_ERROR,
                     "Invalid channel %d specified as output from matrix.\n",
                     s->matrix_out_ch[mat]);
-            return AVERROR_INVALIDDATA;
+            goto error;
         }
         if (frac_bits > 14) {
             av_log(m->avctx, AV_LOG_ERROR,
                     "Too many fractional bits specified.\n");
-            return AVERROR_INVALIDDATA;
+            goto error;
         }
 
         max_chan = s->max_matrix_channel;
@@ -770,6 +769,11 @@ static int read_matrix_params(MLPDecodeContext *m, unsigned int substr, GetBitCo
     }
 
     return 0;
+error:
+    s->num_primitive_matrices = 0;
+    memset(s->matrix_out_ch, 0, sizeof(s->matrix_out_ch));
+
+    return AVERROR_INVALIDDATA;
 }
 
 /** Read channel parameters. */