Checks if there is a tile at the given location (in tile coordinates) in the given layer. Returns false if there is no tile or if the tile at that location has an index of -1.
X position to get the tile from (given in tile units, not pixels).
Y position to get the tile from (given in tile units, not pixels).
The Tilemap Layer to act upon.
Returns a boolean, or null if the layer given was invalid.