avoid crash with empty concavepolygonshape, fixes #3169

servers/physics/shape_sw.cpp

@@ -1354,6 +1354,10 @@ void ConcavePolygonShapeSW::_fill_bvh(_VolumeSW_BVH* p_bvh_tree,BVH* p_bvh_array
 void ConcavePolygonShapeSW::_setup(DVector<Vector3> p_faces) {
 
 	int src_face_count=p_faces.size();
+	if (src_face_count==0) {
+		configure(AABB());
+		return;
+	}
 	ERR_FAIL_COND(src_face_count%3);
 	src_face_count/=3;