gui : fix memset size argument

[Philippe Roussel]

Hi all,

While compiling svn trunk I saw a warning that looked like a real bug.
If I'm not mistaken, here's the fix in its glorious complexity.

Philippe

Index: gui/Source/NSBitmapImageRep+JPEG.m
===================================================================
--- gui/Source/NSBitmapImageRep+JPEG.m  (révision 30131)
+++ gui/Source/NSBitmapImageRep+JPEG.m  (copie de travail)
@@ -553,7 +553,7 @@
       return nil;
     }
 
-  memset((void*)&cinfo, 0, sizeof(struct jpeg_decompress_struct));
+  memset((void*)&cinfo, 0, sizeof(struct jpeg_compress_struct));
 
   imageSource = [self bitmapData];
   sPP = [self samplesPerPixel];