(imagemagick_compute_animated_image): Fix animated segafault

(imagemagick_compute_animated_image): Setting the iterator row to
zero is apparently not allowed.

src/ChangeLog

@@ -2,6 +2,8 @@
 
 	* image.c (imagemagick_compute_animated_image): Animate correctly
 	when sub-images are smaller than the main image.
+	(imagemagick_compute_animated_image): Setting the iterator row to
+	zero is apparently not allowed.
 
 2013-08-15  Jan Djärv  <jan.h.d@swipnet.se>
 

src/image.c

@@ -7945,7 +7945,8 @@ imagemagick_compute_animated_image (MagickWand *super_wand, int ino)
 
       /* The sub-image may not start at origo, so move the destination
 	 iterator to where the sub-image should start. */
-      PixelSetIteratorRow (dest_iterator, source_top);
+      if (source_top > 0)
+	PixelSetIteratorRow (dest_iterator, source_top);
 
       while ((source = PixelGetNextIteratorRow (source_iterator, &source_width))
 	     != NULL)