Remove melting ice timeouts when terrain changes

If special level lua code creates a melting ice timeout, but
later in the code places stairs, or a trap which might change
the ice to room floor, the timer sanity checking doesn't
like that.

src/mklev.c

@@ -1635,6 +1635,9 @@ mkstairs(xchar x, xchar y,
     dest.dlevel = u.uz.dlevel + (up ? -1 : 1);
     stairway_add(x, y, up ? TRUE : FALSE, FALSE, &dest);
 
+    if (levl[x][y].typ == ICE)
+        spot_stop_timers(x, y, MELT_ICE_AWAY);
+
     levl[x][y].typ = STAIRS;
     levl[x][y].ladder = up ? LA_UP : LA_DOWN;
 }

src/trap.c

@@ -348,6 +348,7 @@ maketrap(int x, int y, int typ)
     boolean oldplace;
     struct trap *ttmp;
     struct rm *lev = &levl[x][y];
+    boolean was_ice = (lev->typ == ICE);
 
     if ((ttmp = t_at(x, y)) != 0) {
         if (undestroyable_trap(ttmp->ttyp))
@@ -459,6 +460,8 @@ maketrap(int x, int y, int typ)
                          : DOOR;
 
         unearth_objs(x, y);
+        if (was_ice && lev->typ != ICE)
+            spot_stop_timers(x, y, MELT_ICE_AWAY);
         break;
     }