Don't store TileMapLayer data if empty

doc/classes/TileMapLayer.xml

@@ -268,7 +268,7 @@
 			The quadrant size does not apply on a Y-sorted [TileMapLayer], as tiles are be grouped by Y position instead in that case.
 			[b]Note:[/b] As quadrants are created according to the map's coordinate system, the quadrant's "square shape" might not look like square in the [TileMapLayer]'s local coordinate system.
 		</member>
-		<member name="tile_map_data" type="PackedByteArray" setter="set_tile_map_data_from_array" getter="get_tile_map_data_as_array" default="PackedByteArray(&quot;AAA=&quot;)">
+		<member name="tile_map_data" type="PackedByteArray" setter="set_tile_map_data_from_array" getter="get_tile_map_data_as_array" default="PackedByteArray()">
 			The raw tile map data as a byte array.
 		</member>
 		<member name="tile_set" type="TileSet" setter="set_tile_set" getter="get_tile_set">

scene/2d/tile_map_layer.cpp

@@ -2588,6 +2588,11 @@ TileMapLayer::HighlightMode TileMapLayer::get_highlight_mode() const {
 }
 
 void TileMapLayer::set_tile_map_data_from_array(const Vector<uint8_t> &p_data) {
+	if (p_data.is_empty()) {
+		clear();
+		return;
+	}
+
 	const int cell_data_struct_size = 12;
 
 	int size = p_data.size();
@@ -2630,6 +2635,10 @@ Vector<uint8_t> TileMapLayer::get_tile_map_data_as_array() const {
 	const int cell_data_struct_size = 12;
 
 	Vector<uint8_t> tile_map_data_array;
+	if (tile_map_layer_data.is_empty()) {
+		return tile_map_data_array;
+	}
+
 	tile_map_data_array.resize(2 + tile_map_layer_data.size() * cell_data_struct_size);
 	uint8_t *ptr = tile_map_data_array.ptrw();