Step the game *before* updating vision

Stepping the game after updating the vision could allow creatures like
gormlaks to move *out* of the character's pre-calculated lines of sight,
causing gormlaks right next to the character to be invisible.

src/Xanthous/App.hs

@@ -119,9 +119,9 @@ handleCommand (Move dir) = do
   collisionAt newPos >>= \case
     Nothing -> do
       characterPosition .= newPos
+      stepGame
       describeEntitiesAt newPos
       modify updateCharacterVision
-      stepGame
     Just Combat -> attackAt newPos
     Just Stop -> pure ()
   continue