Solve the program crash issue

[SinCheung]

//recursively add children and all its expanded children to array at position index

• (int) _insertChildren:(NSArray *)children inArray:(NSMutableArray *)array atIndex:(NSUInteger)index{

  [array replaceObjectsInRange:NSMakeRange(index, 0) withObjectsFromArray:children];
  int res = 0;
  int i=0;
  res += children.count;//start set the children count,then through recursive function to calculate the real child node`s children count.

  for (GITreeNode *child in children) {
  if (child.directoryIsExpanded) {
  //here set a var to save the return value of recursive function.
  int count= [self _insertChildren:child.children inArray:array atIndex:index+i+1];
  i += count;
  res += count;//add return value of recursive function,to solve the crash
  // res += child.children.count;
  }
  i++;
  }
  return res;

}