avcodec/magicyuv: correct end of array check in multi VLC parsing

Fixes: out of array write
Fixes: 63390/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MAGICYUV_fuzzer-5144552979431424.fuzz

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

libavcodec/magicyuv.c

@@ -299,7 +299,7 @@ static int magy_decode_slice(AVCodecContext *avctx, void *tdata,
                 return ret;
 
             for (k = 0; k < height; k++)
-                READ_PLANE(dst, i, 1, 5)
+                READ_PLANE(dst, i, 1, 7)
         }
 
         switch (pred) {