[image_picker] Fix clang analyzer warnings in iOS platform code #42678
Description
Steps to Reproduce
$ cd packages/image_picker/example/
$ flutter build ios
$ cd ios
$ /usr/bin/xcodebuild build -workspace Runner.xcworkspace -scheme Runner -configuration Release CODE_SIGN_IDENTITY=- CODE_SIGNING_ALLOWED=NO analyzeLogs
Classes/FLTImagePickerMetaDataUtil.m:45:29: warning: Potential leak of an object stored into 'source'
CGImageSourceRef source = CGImageSourceCreateWithData((CFDataRef)imageData, NULL);
^
1 warning generated.
Looks like there's a missing CFRelease(source);