Merge pull request #9 from SDWebImage/bugfix_encoding_first_frame

Fix the issue when provide a `UIAnimatedImage` and encode it into a static WebP failed

Author: dreampiggy

SDWebImageWebPCoder/Classes/SDImageWebPCoder.m

@@ -464,7 +464,13 @@ - (NSData *)encodedDataWithImage:(UIImage *)image format:(SDImageFormat)format o
     BOOL encodeFirstFrame = [options[SDImageCoderEncodeFirstFrameOnly] boolValue];
     if (encodeFirstFrame || frames.count == 0) {
         // for static single webp image
-        data = [self sd_encodedWebpDataWithImage:image quality:compressionQuality];
+        CGImageRef imageRef = image.CGImage;
+#if SD_UIKIT || SD_WATCH
+        if (!imageRef) {
+            imageRef = image.images.firstObject.CGImage;
+        }
+#endif
+        data = [self sd_encodedWebpDataWithImage:imageRef quality:compressionQuality];
     } else {
         // for animated webp image
         WebPMux *mux = WebPMuxNew();
@@ -473,7 +479,7 @@ - (NSData *)encodedDataWithImage:(UIImage *)image format:(SDImageFormat)format o
         }
         for (size_t i = 0; i < frames.count; i++) {
             SDImageFrame *currentFrame = frames[i];
-            NSData *webpData = [self sd_encodedWebpDataWithImage:currentFrame.image quality:compressionQuality];
+            NSData *webpData = [self sd_encodedWebpDataWithImage:currentFrame.image.CGImage quality:compressionQuality];
             int duration = currentFrame.duration * 1000;
             WebPMuxFrameInfo frame = { .bitstream.bytes = webpData.bytes,
                 .bitstream.size = webpData.length,
@@ -510,14 +516,12 @@ - (NSData *)encodedDataWithImage:(UIImage *)image format:(SDImageFormat)format o
     return data;
 }
 
-- (nullable NSData *)sd_encodedWebpDataWithImage:(nullable UIImage *)image quality:(double)quality {
-    if (!image) {
+- (nullable NSData *)sd_encodedWebpDataWithImage:(nullable CGImageRef)imageRef quality:(double)quality {
+    NSData *webpData;
+    if (!imageRef) {
         return nil;
     }
 
-    NSData *webpData;
-    CGImageRef imageRef = image.CGImage;
-    
     size_t width = CGImageGetWidth(imageRef);
     size_t height = CGImageGetHeight(imageRef);
     if (width == 0 || width > WEBP_MAX_DIMENSION) {