avcodec/vmdaudio: Fix channels count bug

Fixes: division by zero
Fixes: 45811/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VMDAUDIO_fuzzer-6412592581574656
Fixes: 45979/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VMDAUDIO_fuzzer-5362043060879360

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

libavcodec/vmdaudio.c

@@ -85,7 +85,7 @@ static av_cold int vmdaudio_decode_init(AVCodecContext *avctx)
     }
 
     av_channel_layout_uninit(&avctx->ch_layout);
-    av_channel_layout_default(&avctx->ch_layout, channels == 1);
+    av_channel_layout_default(&avctx->ch_layout, channels);
 
     if (avctx->bits_per_coded_sample == 16)
         avctx->sample_fmt = AV_SAMPLE_FMT_S16;