OS_Vth, Verify tri-handle

IN:
     A = Tri-handle subtype
          TH_FILT ($F0), verify filter handle
          TH_WMG ($F1), verify wildcard manager handle
          TH_ALM ($F2), verify alarm handle
     IX = tri-handle

OUT, if call successful:
     Fc = 0, handle OK.
          B = Bank
          H = Adress of high byte
          L = Segment
OUT, if call failed:
     Fc = 1
          A = RC_HAND, bad handle

Registers changed after return:
     ...CDE../IXIY same
     AFB...HL/.... different