BVH - prevent self collisions

I had missed a special case check for userdata of two colliding objects being equal. In this case, collisions should not be reported. This is used in the physics to prevent self intersection in composite objects.

core/math/bvh.h

@@ -472,6 +472,14 @@ private:
 	void _unpair(BVHHandle p_from, BVHHandle p_to) {
 		tree._handle_sort(p_from, p_to);
 
+		typename BVHTREE_CLASS::ItemExtra &exa = tree._extra[p_from.id()];
+		typename BVHTREE_CLASS::ItemExtra &exb = tree._extra[p_to.id()];
+
+		// if the userdata is the same, no collisions should occur
+		if ((exa.userdata == exb.userdata) && exa.userdata) {
+			return;
+		}
+
 		typename BVHTREE_CLASS::ItemPairs &pairs_from = tree._pairs[p_from.id()];
 		typename BVHTREE_CLASS::ItemPairs &pairs_to = tree._pairs[p_to.id()];
 
@@ -481,9 +489,6 @@ private:
 		// callback
 		if (unpair_callback) {
 
-			typename BVHTREE_CLASS::ItemExtra &exa = tree._extra[p_from.id()];
-			typename BVHTREE_CLASS::ItemExtra &exb = tree._extra[p_to.id()];
-
 			unpair_callback(pair_callback_userdata, p_from, exa.userdata, exa.subindex, p_to, exb.userdata, exb.subindex, ud_from);
 		}
 	}
@@ -544,6 +549,14 @@ private:
 		// only have to do this oneway, lower ID then higher ID
 		tree._handle_sort(p_ha, p_hb);
 
+		const typename BVHTREE_CLASS::ItemExtra &exa = _get_extra(p_ha);
+		const typename BVHTREE_CLASS::ItemExtra &exb = _get_extra(p_hb);
+
+		// if the userdata is the same, no collisions should occur
+		if ((exa.userdata == exb.userdata) && exa.userdata) {
+			return;
+		}
+
 		typename BVHTREE_CLASS::ItemPairs &p_from = tree._pairs[p_ha.id()];
 		typename BVHTREE_CLASS::ItemPairs &p_to = tree._pairs[p_hb.id()];
 
@@ -561,9 +574,6 @@ private:
 		void *callback_userdata = nullptr;
 
 		if (pair_callback) {
-			const typename BVHTREE_CLASS::ItemExtra &exa = _get_extra(p_ha);
-			const typename BVHTREE_CLASS::ItemExtra &exb = _get_extra(p_hb);
-
 			callback_userdata = pair_callback(pair_callback_userdata, p_ha, exa.userdata, exa.subindex, p_hb, exb.userdata, exb.subindex);
 		}