Remove the compression quality when have max file size limit, and update the test cases for JPEG

SDWebImage/Core/SDImageCoder.h

@@ -73,7 +73,7 @@ FOUNDATION_EXPORT SDImageCoderOption _Nonnull const SDImageCoderEncodeMaxPixelSi
 
 /**
  A NSUInteger value specify the max ouput data bytes size after encoding. Some lossy format like JPEG/HEIF supports the hint for codec to automatically reduce the quality and match the file size you want. Note this option will override the `SDImageCoderEncodeCompressionQuality`, because now the quality is decided by the encoder. (NSNumber)
- @note Not all format supports this feature. And this options does not works for vector images.
+ @note This is a hint, no gurantee for output size because of compression algorithm limit. And this options does not works for vector images.
  @note works for `SDImageCoder`
  */
 FOUNDATION_EXPORT SDImageCoderOption _Nonnull const SDImageCoderEncodeMaxFileSize;

SDWebImage/Core/SDImageIOAnimatedCoder.m

@@ -467,6 +467,8 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     NSUInteger maxFileSize = [options[SDImageCoderEncodeMaxFileSize] unsignedIntegerValue];
     if (maxFileSize > 0) {
         properties[kSDCGImageDestinationRequestedFileSize] = @(maxFileSize);
+        // Remove the quality if we have file size limit
+        properties[(__bridge NSString *)kCGImageDestinationLossyCompressionQuality] = nil;
     }
     
     BOOL encodeFirstFrame = [options[SDImageCoderEncodeFirstFrameOnly] boolValue];

SDWebImage/Core/SDImageIOCoder.m

@@ -291,6 +291,8 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     NSUInteger maxFileSize = [options[SDImageCoderEncodeMaxFileSize] unsignedIntegerValue];
     if (maxFileSize > 0) {
         properties[kSDCGImageDestinationRequestedFileSize] = @(maxFileSize);
+        // Remove the quality if we have file size limit
+        properties[(__bridge NSString *)kCGImageDestinationLossyCompressionQuality] = nil;
     }
     
     // Add your image to the destination.

Tests/Tests/SDImageCoderTests.m

@@ -98,6 +98,26 @@
     expect(testColor.sd_hexString).equal(backgroundColor.sd_hexString);
 }
 
+- (void)test09ThatJPGImageEncodeWithMaxFileSize {
+    NSString * testImagePath = [[NSBundle bundleForClass:[self class]] pathForResource:@"TestImageLarge" ofType:@"jpg"];
+    UIImage *image = [[UIImage alloc] initWithContentsOfFile:testImagePath];
+    // This large JPEG encoding size between (770KB ~ 2.23MB)
+    NSUInteger limitFileSize = 1 * 1024 * 1024; // 1MB
+    // 100 quality (biggest)
+    NSData *maxEncodedData = [SDImageCodersManager.sharedManager encodedDataWithImage:image format:SDImageFormatJPEG options:nil];
+    expect(maxEncodedData).notTo.beNil();
+    expect(maxEncodedData.length).beGreaterThan(limitFileSize);
+    // 0 quality (smallest)
+    NSData *minEncodedData = [SDImageCodersManager.sharedManager encodedDataWithImage:image format:SDImageFormatJPEG options:@{SDImageCoderEncodeCompressionQuality : @(0)}];
+    expect(minEncodedData).notTo.beNil();
+    expect(minEncodedData.length).beLessThan(limitFileSize);
+    NSData *limitEncodedData = [SDImageCodersManager.sharedManager encodedDataWithImage:image format:SDImageFormatJPEG options:@{SDImageCoderEncodeMaxFileSize : @(limitFileSize)}];
+    expect(limitEncodedData).notTo.beNil();
+    // So, if we limit the file size, the output data should in (770KB ~ 2.23MB)
+    expect(limitEncodedData.length).beLessThan(maxEncodedData.length);
+    expect(limitEncodedData.length).beGreaterThan(minEncodedData.length);
+}
+
 - (void)test11ThatAPNGPCoderWorks {
     NSURL *APNGURL = [[NSBundle bundleForClass:[self class]] URLForResource:@"TestImageAnimated" withExtension:@"apng"];
     [self verifyCoder:[SDImageAPNGCoder sharedCoder]