Fix crash when notifying released observer.

Reproduced like so:

* On iPhone, select "Photos".
* Move ahead to a photo that fails to load.
* Back to "Root".
* Select "Photos" again.
* Move ahead to the same photo that fails to load.
* Watch it crash.

Demo iPhone/EGOPhotoViewer/Classes/Views/EGOPhotoImageView/EGOPhotoImageView.m

@@ -318,7 +318,8 @@ - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)vi
 - (void)dealloc {
 
 	NSLog(@"dealloc EGOPhotoImageView");
-
+
+	[[EGOImageLoader sharedImageLoader] removeObserver:self forURL:self.photo.imageURL];
 	[[EGOImageLoader sharedImageLoader] cancelLoadForURL:self.photo.imageURL];
 
 	[_imageView release]; _imageView=nil;