obs-ffmpeg: Enable file splitting with obs_data directly

Also modifies UI accordingly.

This can enable file splitting even if no time or storage limit is set.

UI/window-basic-main-outputs.cpp

@@ -1937,6 +1937,7 @@ bool AdvancedOutput::StartRecording()
 			obs_data_set_bool(settings, "allow_spaces", !noSpace);
 			obs_data_set_bool(settings, "allow_overwrite",
 					  overwriteIfExists);
+			obs_data_set_bool(settings, "split_file", true);
 			obs_data_set_int(settings, "max_time_sec",
 					 splitFileTime * 60);
 			obs_data_set_int(settings, "max_size_mb",

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

@@ -400,8 +400,7 @@ static bool ffmpeg_mux_start(void *data)
 			obs_data_get_int(settings, "max_time_sec") * 1000000LL;
 		stream->max_size = obs_data_get_int(settings, "max_size_mb") *
 				   (1024 * 1024);
-		stream->split_file = stream->max_time > 0 ||
-				     stream->max_size > 0;
+		stream->split_file = obs_data_get_bool(settings, "split_file");
 		stream->reset_timestamps =
 			obs_data_get_bool(settings, "reset_timestamps");
 		stream->allow_overwrite =