obs-ffmpeg/ffmpeg-mux: Fix issue with HLS

For some reason, currently unknown, FFmpeg logging has to be set to
something in order for HLS to not fail on Windows, even if it's just an
empty function.

(Author comment: I don't feel comfortable not knowing why, my theory is
that FFmpeg has an issue with this internally with HLS on Windows
related to logging or how it's trying to log, I have absolutely no idea
what's going on and if someone can enlighten me or debug FFmpeg itself
it'd be real nice to know why.)

plugins/obs-ffmpeg/ffmpeg-mux/ffmpeg-mux.c

@@ -231,6 +231,7 @@ static bool get_audio_params(struct audio_params *audio, int *argc,
 static void ffmpeg_log_callback(void *param, int level, const char *format,
 				va_list args)
 {
+#ifdef DEBUG_FFMPEG
 	char out_buffer[4096];
 	struct dstr out = {0};
 
@@ -257,6 +258,11 @@ static void ffmpeg_log_callback(void *param, int level, const char *format,
 	}
 
 	dstr_free(&out);
+#else
+	UNUSED_PARAMETER(level);
+	UNUSED_PARAMETER(format);
+	UNUSED_PARAMETER(args);
+#endif
 	UNUSED_PARAMETER(param);
 }
 
@@ -337,9 +343,7 @@ static bool init_params(int *argc, char ***argv, struct main_params *params,
 			     "{stream_key}");
 	}
 
-#ifdef DEBUG_FFMPEG
 	av_log_set_callback(ffmpeg_log_callback);
-#endif
 
 	get_opt_str(argc, argv, &params->muxer_settings, "muxer settings");