fix crash

YYWebImage/Categories/UIImageView+YYWebImage.m

@@ -152,9 +152,9 @@ static int _YYWebImageHighlightedSetterKey;
             YYWebImageCompletionBlock _completion = ^(UIImage *image, NSURL *url, YYWebImageFromType from, YYWebImageStage stage, NSError *error) {
                 __strong typeof(_self) self = _self;
                 BOOL setImage = (stage == YYWebImageStageFinished || stage == YYWebImageStageProgress) && image && !(options & YYWebImageOptionAvoidSetImage);
-                BOOL showFade = ((options & YYWebImageOptionSetImageWithFadeAnimation) && !self.highlighted);
                 dispatch_async(dispatch_get_main_queue(), ^{
                     if (setImage && self) {
+                        BOOL showFade = ((options & YYWebImageOptionSetImageWithFadeAnimation) && !self.highlighted);
                         if (showFade) {
                             CATransition *transition = [CATransition animation];
                             transition.duration = stage == YYWebImageStageFinished ? _YYWebImageFadeTime : _YYWebImageProgressiveFadeTime;