another getobj/force_invmenu fix

For !force_invmenu when attempting a command that needs an object,
if inventory is completely empty
 What do you want to <foo>? [*]
will report "Never mind" and stop asking if player presses return
or report "Not carrying anything" and reprompt if player types '*'.
But for force_invmenu, it would report
 Not carrying anything.  Never mind.
without any reprompting in between the two messages.  Just skip
the second message in that situation.

Perhaps the first case should avoid reprompting too but I haven't
gone that far.

src/invent.c

@@ -1632,8 +1632,11 @@ getobj(const char *word,
             ilet = display_pickinv(allowed_choices, *qbuf ? qbuf : (char *) 0,
                                    menuquery,
                                    TRUE, allowcnt ? &ctmp : (long *) 0);
-            if (!ilet)
+            if (!ilet) {
+                if (oneloop)
+                    return (struct obj *) 0;
                 continue;
+            }
             if (ilet == HANDS_SYM)
                 return (struct obj *) &cg.zeroobj; /* cast away 'const' */
             if (ilet == '\033') {