avcodec/ac3dec: Check that the number of channels with dependant streams is valid

Fixes: left shift of 1 by 63 places cannot be represented in type 'long long'
Fixes: out of array access
Fixes: 7284/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AC3_fuzzer-5767914968842240

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit e3275f937d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ac3dec.c

@@ -1702,6 +1702,11 @@ dependent_frame:
                 channel_layout |= custom_channel_map_locations[ch][1];
             }
         }
+        if (av_get_channel_layout_nb_channels(channel_layout) > EAC3_MAX_CHANNELS) {
+            av_log(avctx, AV_LOG_ERROR, "Too many channels (%d) coded\n",
+                   av_get_channel_layout_nb_channels(channel_layout));
+            return AVERROR_INVALIDDATA;
+        }
 
         avctx->channel_layout = channel_layout;
         avctx->channels = av_get_channel_layout_nb_channels(channel_layout);