Magic portals and levitation boots

From a bug report.  Removing levitation boots while hovering over
a magic portal causes the portal to be delayed since it takes time to
remove the boots.  This causes the portal to be taken via unmul in allmain.
At that point, the will activation message display but you won't teleport
until you type something.  Handle the delayed goto after unmul completes.

src/allmain.c

@@ -283,10 +283,13 @@ moveloop()
 
 		    /* when immobile, count is in turns */
 		    if(multi < 0) {
-			if (++multi == 0)	/* finished yet? */
+			if (++multi == 0) {	/* finished yet? */
 			    unmul((char *)0);
+			    /* if unmul caused a level change, take it now */
+			    if (u.utotype) deferred_goto();
+			}
 		    }
-		}			
+		}
 	    } while (youmonst.movement<NORMAL_SPEED); /* hero can't move loop */
 
 	    /******************************************/