### Godot version

5ee983188de97ae027f9b9c1443438063f708a7e

### System information

Windows 11

### Issue description

Godot editor will throw an error and fail to generate preview icons for terrain tiles which use a base image which is not RGBA8 format.
`core\io\image.cpp:2788 - Condition "format != p_src->format" is true.`

### Steps to reproduce

- Import a non-RGBA8 image into Godot.
- Create a TileMap
- Create an associated TileSet
- Create a terrain for this tileset
- Add the image as an atlas
- Go to the paint tab
- Paint the terrain on the TileSet
- An error will occur any time terrains are edited in the TileSet editor or selected in the TileMap editor terrain tab.

### Minimal reproduction project

[tileset_terrain_bug.zip](https://github.com/godotengine/godot/files/13264213/tileset_terrain_bug.zip)

ERR_FAIL_INDEX(p_layer_id, physics.size());
	physics.write[p_layer_id].angular_velocity = p_velocity;
	emit_signal(SNAME("changed"));
}
real_t TileData::get_constant_angular_velocity(int p_layer_id) const {
	ERR_FAIL_INDEX_V(p_layer_id, physics.size(), 0.0);
	return physics[p_layer_id].angular_velocity;
}
void TileData::set_collision_polygons_count(int p_layer_id, int p_polygons_count) {
	ERR_FAIL_INDEX(p_layer_id, physics.size());
	ERR_FAIL_COND(p_polygons_count < 0);
	if (p_polygons_count == physics.write[p_layer_id].polygons.size()) {
		return;
	}
	physics.write[p_layer_id].polygons.resize(p_polygons_count);
	notify_property_list_changed();
	emit_signal(SNAME("changed"));
}
int TileData::get_collision_polygons_count(int p_layer_id) const {
	ERR_FAIL_INDEX_V(p_layer_id, physics.size(), 0);
	return physics[p_layer_id].polygons.size();
}
void TileData::add_collision_polygon(int p_layer_id) {
	ERR_FAIL_INDEX(p_layer_id, physics.size());
	physics.write[p_layer_id].polygons.push_back(PhysicsLayerTileData::PolygonShapeTileData());
	emit_signal(SNAME("changed"));
}
void TileData::remove_collision_polygon(int p_layer_id, int p_polygon_index) {