Fix seqno mismatch and use-after-free in shp_sweep()

The code wrote the swept sector after calling shp_check_one_mines().
This failed to use up the mine that hit the minesweeper, and triggered
a seqno mismatch oops.

The code wrote the minesweeper after calling shp_check_one_mines().
This used freed memory when the minesweeper got sunk there.

Broken in 4.0.17.  Fix by moving both calls before
shp_check_one_mines().
(cherry picked from commit b0644e822c)

src/lib/subs/shpsub.c

@@ -237,13 +237,13 @@ shp_sweep(struct emp_qelem *ship_list, int verbose, int takemob, natid actor)
 	}
 	sect.sct_mines = mines;
 	mlp->unit.ship.shp_item[I_SHELL] = shells;
+	putship(mlp->unit.ship.shp_uid, &mlp->unit.ship);
+	putsect(&sect);
 	if (shp_check_one_mines(mlp)) {
 	    stopping = 1;
 	    emp_remque(qp);
 	    free(qp);
 	}
-	putship(mlp->unit.ship.shp_uid, &mlp->unit.ship);
-	putsect(&sect);
     }
     if (changed)
 	writemap(actor);