Crash instead of returning an invalid index value

[madmiraal]

Currently, when a new BVH leaf item is requested, if the BVH leaf is full, a value of -1 is returned.
The compiler is raising a array subscript 4294967295 is above array bounds warning when this value is used as an index in an array of fixed size:

In file included from ./core/math/bvh_tree.h:168,
                 from ./core/math/bvh.h:25,
                 from servers/physics_2d/broad_phase_2d_bvh.h:11,
                 from servers/physics_2d/broad_phase_2d_bvh.cpp:7:
In member function 'BVH_ABB<BOUNDS, POINT>& BVH_Tree<T, MAX_CHILDREN, MAX_ITEMS, USE_PAIRS, BOUNDS, POINT>::TLeaf::get_aabb(uint32_t) [with T = CollisionObject2DSW; int MAX_CHILDREN = 2; int MAX_ITEMS = 128; bool USE_PAIRS = true; BOUNDS = Rect2; POINT = Vector2]',
    inlined from 'bool BVH_Tree<T, MAX_CHILDREN, MAX_ITEMS, USE_PAIRS, BOUNDS, POINT>::_node_add_item(uint32_t, uint32_t, const BVH_ABB<BOUNDS, POINT>&) [with T = CollisionObject2DSW; int MAX_CHILDREN = 2; int MAX_ITEMS = 128; bool USE_PAIRS = true; BOUNDS = Rect2; POINT = Vector2]' at ./core/math/bvh_tree.h:439:22,
    inlined from 'BVHHandle BVH_Tree<T, MAX_CHILDREN, MAX_ITEMS, USE_PAIRS, BOUNDS, POINT>::item_add(T*, bool, const BOUNDS&, int32_t, bool, uint32_t, uint32_t, bool) [with T = CollisionObject2DSW; int MAX_CHILDREN = 2; int MAX_ITEMS = 128; bool USE_PAIRS = true; BOUNDS = Rect2; POINT = Vector2]' at ./core/math/bvh_public.inc:84:36,
    inlined from 'BVHHandle BVH_Manager<T, USE_PAIRS, MAX_ITEMS, BOUNDS, POINT, BVH_THREAD_SAFE>::create(T*, bool, const BOUNDS&, int, bool, uint32_t, uint32_t) [with T = CollisionObject2DSW; bool USE_PAIRS = true; int MAX_ITEMS = 128; BOUNDS = Rect2; POINT = Vector2; bool BVH_THREAD_SAFE = true]' at ./core/math/bvh.h:119:36,
    inlined from 'virtual BroadPhase2DSW::ID BroadPhase2DBVH::create(CollisionObject2DSW*, int, const Rect2&, bool)' at servers/physics_2d/broad_phase_2d_bvh.cpp:18:24:
./core/math/bvh_structs.inc:48:21: error: array subscript 4294967295 is above array bounds of 'BVH_ABB<Rect2, Vector2> [128]' [-Werror=array-bounds=]
   48 |         return aabbs[p_id];
      |                ~~~~~^

The only time a leaf item is requested is when an item is added to a node, and, in debug builds, the returned value is checked and Rebel Engine will crash if it equals 0xffffffff (the overflowed value of -1 for an unsigned 32 bit integer is 4294967295):

RebelEngine/core/math/bvh_tree.h

Lines 435 to 436 in 0ded452

	ref.item_id = leaf.request_item();
	BVH_ASSERT(ref.item_id != BVHCommon::INVALID);

RebelEngine/core/math/bvh_tree.h

Line 63 in 0ded452

static const uint32_t INVALID = (0xffffffff);

RebelEngine/core/math/bvh_tree.h

Lines 45 to 50 in 0ded452

	// debug only assert
	#ifdef BVH_CHECKS
	#define BVH_ASSERT(a) CRASH_COND((a) == false)
	#else
	#define BVH_ASSERT(a)
	#endif

It appears that it is currently assumed that no attempt will be made to add an item to a node that is full (and that the node is a leaf node). Addressing the dependence on this assumption will require significant changes to the BVH code. In the meantime, it is easier to simply crash if any attempt is made to request an item from a full leaf node.

This PR cause Rebel Engine to crash whenever a leaf item is requested from a full leaf node; instead of only in debug builds.