HUD: Update selection mesh every frame

[appgurueu]

Fixes #11904, most likely also fixes #3873

Minetest incorrectly made the assumption that the selectionbox doesn't change when the pointed thing doesn't change, which doesn't hold in the case of entities (which may have their properties changed) and nodes (which may have their neighborhood changed).

This PR fixes this by always updating the selection mesh. The performance impact is presumably negligible; worst-case performance (pointed thing constantly changing) hasn't changed at all. Only updating the selection mesh when it has changed would require way more code complexity and probably be less efficient.

[rubenwardy]

Could this also fix #3873 ?

[appgurueu]

Could this also fix #3873 ?

Unless updateSelectionMesh is broken it definitely should. Looking at the code that handles comparison of pointed things, I'm very surprised that this code worked in the first place:

bool PointedThing::operator==(const PointedThing &pt2) const
{
	if (type != pt2.type)
	{
		return false;
	}
	if (type == POINTEDTHING_NODE)
	{
		if ((node_undersurface != pt2.node_undersurface)
				|| (node_abovesurface != pt2.node_abovesurface)
				|| (node_real_undersurface != pt2.node_real_undersurface))
			return false;
	}
	else if (type == POINTEDTHING_OBJECT)
	{
		if (object_id != pt2.object_id)
			return false;
	}
	return true;
}

for nodes it only compares position and direction, for objects only object ID. I assume that worked for doors in most of the cases because flipping a door is very likely to make you either (1) point another face of the door or (2) point another node.

For logging it's probably fine, although it shouldn't check direction there IMO (another log line just because you pointed another face seems odd to me).

[SmallJoker]

No noticeable "Draw scene" or "drawtime" increase. Works as expected.