Fixed UNGAP bug

Fixed a bug where if you called UNGAP and there were two gaps in
sequence (eg. ‘(SEE AGENT AG002 OBJECT OBJ002)), the second gap would
not be enclosed in a list.
eg.
‘(OBJECT HUMAN F-NAME (CHARLES) L-NAME NIL GENDER (MALE))
instead of the correct
‘(OBJECT (HUMAN F-NAME (CHARLES) L-NAME NIL GENDER (MALE)))