avcodec/mjpegdec: Restore non bayer checks in ljpeg_decode_rgb_scan()

Fixes: out of array write
Fixes: 17088/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEGLS_fuzzer-5654877765632000

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

libavcodec/mjpegdec.c

@@ -1071,6 +1071,10 @@ static int ljpeg_decode_rgb_scan(MJpegDecodeContext *s, int nb_components, int p
     int resync_mb_x = 0;
     int vpred[6];
 
+    if (!s->bayer && s->nb_components < 3)
+        return AVERROR_INVALIDDATA;
+    if (s->bayer && s->nb_components > 2)
+        return AVERROR_INVALIDDATA;
     if (s->nb_components <= 0 || s->nb_components > 4)
         return AVERROR_INVALIDDATA;
     if (s->v_max != 1 || s->h_max != 1 || !s->lossless)