Handle palette underflows, fill remaining space with black (zero) data.

Patch by Sebastian Vater <cdgs basty googlemail com>.

Originally committed as revision 23111 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/iff.c

@@ -123,10 +123,8 @@ int ff_cmap_read_palette(AVCodecContext *avctx, uint32_t *pal)
     }
 
     count = 1 << avctx->bits_per_coded_sample;
-    if (avctx->extradata_size < count * 3) {
-        av_log(avctx, AV_LOG_ERROR, "palette data underflow\n");
-        return AVERROR_INVALIDDATA;
-    }
+    // If extradata is smaller than actually needed, fill the remaining with black.
+    count = FFMIN(avctx->extradata_size / 3, count);
     for (i=0; i < count; i++) {
         pal[i] = 0xFF000000 | AV_RB24( avctx->extradata + i*3 );
     }