Fix launch not to wipe out target ship updates

Ships can expend shells to defend against missiles, in
shp_missile_defense().  Any shell use by the target ship got wiped out
when launch_missile() wrote back the target ship, triggering a seqno
mismatch oops.

Fix by re-reading the target ship.

src/lib/commands/laun.c

@@ -276,6 +276,7 @@ launch_missile(struct plnstr *pp)
 		       target_ship.shp_x, target_ship.shp_y,
 		       target_ship.shp_own, &sublaunch) < 0)
 	    return RET_OK;
+	getship(n, &target_ship);
 	if (!msl_hit(pp, shp_hardtarget(&target_ship), EF_SHIP,
 		     N_SHP_MISS, N_SHP_SMISS, sublaunch,
 		     target_ship.shp_own)) {