NAME: THM_CHECK_TVAR (FUNCTION) PURPOSE: This routine check whether the given tplot variable TVAR exists in the memory. If not, return 0. Otherwise, then check whether it contains data of the current date. If yes, return 1. If not, return 0. ARGUMENTS: tvar: (INPUT, REQUIRED) The name of a tplot variable to be checked. KEYWORDS: None. HISTORY: 2009-05-10: written by Jianbao Tao, in CU/LASP.