Fix a random disconnect (#5292)

This almost never happens but since the flood uses this method extensively, everyone gets disconnected every hour or so so I fixed it myself.

core/src/mindustry/world/Tile.java

@@ -628,6 +628,7 @@ public class Tile implements Position, QuadTreeObject, Displayable{
 
     @Remote(called = Loc.server)
     public static void setTile(Tile tile, Block block, Team team, int rotation){
+        if(tile == null) return;
         tile.setBlock(block, team, rotation);
     }