avcodec/tiff: Check for planar DNG images

The DNG code hardcodes plane 0 at some places, so its better to disallow cases
that have more planes.

Fixes: eg_crash
Found-by: 黄宁 <tsukimurarin@163.com>
Reviewed-by: Nick Renieris <velocityra@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/tiff.c

@@ -1874,6 +1874,8 @@ again:
         bps = s->bpp / s->bppcount;
         if (bps < 8 || bps > 32)
             return AVERROR_INVALIDDATA;
+        if (s->planar)
+            return AVERROR_PATCHWELCOME;
     }
 
     if (!s->is_tiled && !s->strippos && !s->stripoff) {