Fix a bug where erasing cells with "Match Corners" mode would not result in all neighbors updating correctly

Author: IphStich

scene/2d/tile_map_layer.cpp

@@ -2601,7 +2601,7 @@ HashMap<Vector2i, TileSet::TerrainsPattern> TileMapLayer::terrain_fill_pattern(c
 		// Find the adequate neighbor.
 		for (int j = 0; j < TileSet::CELL_NEIGHBOR_MAX; j++) {
 			TileSet::CellNeighbor bit = TileSet::CellNeighbor(j);
-			if (tile_set->is_valid_terrain_peering_bit(p_terrain_set, bit)) {
+			if (tile_set->is_existing_neighbor(bit)) {
 				Vector2i neighbor = tile_set->get_neighbor_cell(coords, bit);
 				if (!can_modify_set.has(neighbor)) {
 					can_modify_list.push_back(neighbor);