monster pick up fix

[Tony Elmroth <elmroth@math.chalmers.se>]

If the only thing carried is an invisible force the 
game dumps at pickup (mostly done by demons).

Tony


*** crossfire-0.88.0.orig/object.c	Sun Dec 20 05:49:38 1992
--- crossfire-0.88.0/object.c	Fri Jan  8 23:08:33 1993
***************
*** 817,825 ****
            tmp=tmp->below;
        while (tmp->below!=NULL&&tmp->below->type==op->type)
            tmp=tmp->below;
!       while(tmp!=NULL&&tmp->invisible)
            tmp=tmp->above;
!       if (tmp->below!=NULL) {
            tmp->below->above=op;
            op->below=tmp->below;
            tmp->below=op;
--- 817,831 ----
            tmp=tmp->below;
        while (tmp->below!=NULL&&tmp->below->type==op->type)
            tmp=tmp->below;
!       while(tmp->above!=NULL&&tmp->invisible)
            tmp=tmp->above;
! 
!       if (tmp->above==NULL && tmp->invisible) {
! 	where->inv = op;
! 	op->above = NULL;
! 	op->below = tmp;
! 	tmp->above = op;
!       } else if (tmp->below!=NULL) {
            tmp->below->above=op;
            op->below=tmp->below;
            tmp->below=op;