Fix doxy and assert().

Originally committed as revision 22040 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/rectangle.h

@@ -37,11 +37,11 @@
  * fill a rectangle.
  * @param h height of the rectangle, should be a constant
  * @param w width of the rectangle, should be a constant
- * @param size the size of val (1 or 4), should be a constant
+ * @param size the size of val (1, 2 or 4), should be a constant
  */
 static av_always_inline void fill_rectangle(void *vp, int w, int h, int stride, uint32_t val, int size){
     uint8_t *p= (uint8_t*)vp;
-    assert(size==1 || size==4);
+    assert(size==1 || size==2 || size==4);
     assert(w<=4);
 
     w      *= size;