file_id	IN:	File identifier returned by Hopen
	isfirst	IN:	Determines the file label the retrieved length information applies to

	Purpose	Returns the length of a file label.
	Return value	Returns the length of the file label if successful and FAIL (or -1) otherwise.
	Description	When DFANgetfidlen is first called for a given file, it returns the length of the first file label. In order to retrieve the lengths of successive file labels, DFANgetfid must be called between calls to DFANgetfidlen. Otherwise, successive calls to DFANgetfidlen will return the length of the same file label.
		Valid values of isfirst are: 1 to read the first label, and 0 to read the next label.

	FORTRAN	integer function dagfidl(file_id, isfirst)
		integer file_id, isfirst