expand_root: some new_children pointers are not assigned

[arcsinY]

Hi,

In function "expand_root" (alex.h), you use two variables named "in_bounds_new_nodes_start" and "in_bounds_new_nodes_end" to control the boundary of "root->children_". So some elements in "root->children_" will not be assigned to a pointers. However, in function "expand" (alex_nodes.h), all elements of "children_" of a model node will be traversed, and then it will visit null pointers.

Is is right? It seems that we should check whether a elements of "children_" is null when we expand a model node.

Thank you