Only memset for palettes of 16 elements.

Originally committed as revision 20377 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/pcx.c

@@ -71,6 +71,7 @@ static void pcx_palette(const uint8_t **src, uint32_t *dst, unsigned int pallen)
 
     for (i=0; i<pallen; i++)
         *dst++ = bytestream_get_be24(src);
+    if (pallen < 256)
     memset(dst, 0, (256 - pallen) * sizeof(*dst));
 }