Fix vision when vault guard corridor vanishes

src/vault.c

@@ -978,6 +978,7 @@ gd_move(struct monst *grd)
                 (void) rloc(grd, RLOC_MSG);
                 levl[m][n].typ = egrd->fakecorr[0].ftyp;
                 levl[m][n].flags = egrd->fakecorr[0].flags;
+                recalc_block_point(m, n); /* guard corridor goes away */
                 del_engr_at(m, n);
                 newsym(m, n);
                 grd->mpeaceful = 0;