Fixing Scale Mode (None) in previews (#182)

* Handle SCALE_NONE mode when optimized for previews (previews are often smaller than the project size)

* Fixing 2 memory leaks (thanks PeterM)

src/FFmpegReader.cpp

@@ -1973,6 +1973,7 @@ void FFmpegReader::RemoveAVFrame(AVFrame* remove_frame)
     {
         // Free memory
 		av_freep(&remove_frame->data[0]);
+		AV_FREE_FRAME(&remove_frame);
 	}
 }