Potential fix for T38111: Duplicating BOIDS emitter cause glitchy operation

Need to reset cached KD tree when duplicating particle system.

source/blender/blenkernel/intern/object.c

@@ -1282,6 +1282,7 @@ static ParticleSystem *copy_particlesystem(ParticleSystem *psys)
 	psysn->frand = NULL;
 	psysn->pdd = NULL;
 	psysn->effectors = NULL;
+	psysn->tree = NULL;
 	
 	psysn->pathcachebufs.first = psysn->pathcachebufs.last = NULL;
 	psysn->childcachebufs.first = psysn->childcachebufs.last = NULL;