Use avcodec_free_context() instead of avcodec_close()

This is stated in ffmpeg api documentation:
`Do not use this function. Use avcodec_free_context() to destroy a codec context (either open or closed). Opening and closing a codec context multiple times is not supported anymore – use multiple codec contexts instead.`

av_freep -calls are also performed inside avcodec_free_context() so remove them

codec.c

@@ -249,8 +249,7 @@ void CodecVideoClose(VideoDecoder * video_decoder)
 
     if (video_decoder->VideoCtx) {
 	pthread_mutex_lock(&CodecLockMutex);
-	avcodec_close(video_decoder->VideoCtx);
-	av_freep(&video_decoder->VideoCtx);
+	avcodec_free_context(&video_decoder->VideoCtx);
 	pthread_mutex_unlock(&CodecLockMutex);
     }
 }
@@ -454,8 +453,7 @@ void CodecAudioClose(AudioDecoder * audio_decoder)
     }
     if (audio_decoder->AudioCtx) {
 	pthread_mutex_lock(&CodecLockMutex);
-	avcodec_close(audio_decoder->AudioCtx);
-	av_freep(&audio_decoder->AudioCtx);
+	avcodec_free_context(&audio_decoder->AudioCtx);
 	pthread_mutex_unlock(&CodecLockMutex);
     }
 }