drop and fly from carrier can fail to load last civ or mil

pln_equip() refuses to abandon its base sector.  Unfortunately, it
checks even when flying off carriers, and refuses to load the last
civilian or military depending on what happens to be in uninitialized
variable sect.

Broken in commit 91139692, v4.3.0.

src/lib/subs/plnsub.c

@@ -720,6 +720,9 @@ pln_equip(struct plist *plp, struct ichrstr *ip, char mission)
 					 plp->plane.pln_y,
 					 I_SHELL, needed);
 #endif
+	if (pp->pln_ship >= 0 || pp->pln_land >= 0)
+	    abandon_needed = 0;
+	else
 	    abandon_needed = !!would_abandon(&sect, itype, needed, NULL);
 	if (item[itype] < needed + abandon_needed) {
 	    pr("Not enough %s for %s\n", ichr[itype].i_name, prplane(pp));