EP_Image ($33) - Return pointer to start of file contents

IN:
     A = EP_IMAGE
   BHL = pointer to Eprom File Entry in card at slot (B contains embedded slot mask)

OUT:
   Fc = 0, File Eprom available, File Entry available
        BHL = pointer to start of file image

   Fc = 1,
        A = RC_Onf
        File Eprom was not found in slot, or File Entry not available

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