[macOS] Fix typo in render size change check condition
[macOS] Fix typo in render size change check condition

Analogically to fix for iOS in pull request #215.

flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc,flutter-webrtc/flutter-webrtc