EP_Find ($0C) - Find active File(name) in File Area in slot C

IN:
    A = EP_FIND
    C = slot number of File Eprom (Area)
   DE = pointer to null-terminated filename to be searched for.
        The filename is excl. device name and must begin with '/'.

OUT:
   Fc = 0, File Eprom available
        Fz = 1, File Entry found.
             BHL = pointer to File Entry in card at slot
        Fz = 0, No file were found on the File Eprom.
             BHL = pointer to free byte on File Eprom in slot

   Fc = 1,
        A = RC_Onf
        File Eprom was not found at slot C

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