Merge pull request SDWebImage#3760 from lukmccall/patch-1

Fix `sd_imageFormat` sometimes returns `undefined`

Author: dreampiggy

SDWebImage/Core/SDAnimatedImage.m

@@ -182,6 +182,8 @@ - (instancetype)initWithData:(NSData *)data scale:(CGFloat)scale options:(SDImag
 #else
         self = [super initWithCGImage:image.CGImage scale:MAX(scale, 1) orientation:image.imageOrientation];
 #endif
+        // Defines the associated object that holds the format for static images
+        super.sd_imageFormat = format;
         return self;
     }
 }
@@ -374,10 +376,6 @@ - (SDImageFormat)sd_imageFormat {
     }
 }
 
-- (void)setSd_imageFormat:(SDImageFormat)sd_imageFormat {
-    return;
-}
-
 - (BOOL)sd_isVector {
     return NO;
 }