GN_Flc, close filter

RST 20H, DEFW $2409

IN:

     IX = filter handle

     Fc = 0
     IX = 0
     BC = number of input characters written to filter
     (BC = 0 provided at least one character has been read)
     DE = number of characters read from filter

     Fc = 1
     A = error code:
          RC_HAND ($08), IX(in) was not a valid filter handle

     ......HL/..IY same
     AFBCDE../IX.. different

Bugs:
 

Related calls:

GN_Flf, flush filter
GN_Flo, open filter
GN_Flr, read from filter
GN_Flw, write character to filter
GN_Fpb, push back into filter