Merge pull request #3043 from dreampiggy/fix_ios14_animated_image_static_render

Fix the issue that SDAnimatedImageView can not render static image on iOS 14.

SDWebImage/Core/SDAnimatedImageView.m

@@ -466,6 +466,9 @@
 - (void)displayLayer:(CALayer *)layer
 {
     UIImage *currentFrame = self.currentFrame;
+    if (!currentFrame) {
+        currentFrame = self.image;
+    }
     if (currentFrame) {
         layer.contentsScale = currentFrame.scale;
         layer.contents = (__bridge id)currentFrame.CGImage;