DataFolderExists for data folder references

/// Checks if the datafolder referenced by dfr exists.
/// Unlike DataFolderExists() a dfref pointing to an empty ("") dataFolder is considered non-existing here.
/// @returns one if dfr is valid and references an existing datafolder, zero otherwise
Function DataFolderExistsDFR(dfr)
	dfref dfr

	string dataFolder

	switch(DataFolderRefStatus(dfr))
		case 0: // invalid ref, does not exist
			return 0
		case 1: // might be valid
			dataFolder = GetDataFolder(1,dfr)
			return cmpstr(dataFolder,"") != 0 && DataFolderExists(dataFolder)
		case 3: // free data folders always exist
			return 1
		default:
			Abort "unknown status"
			return 0
	endswitch
End