Fix an issue where modifying a snapshot or unknown circumstances caused node.children to be None

[Mejituu]

#62 #59 #58 node children python TypeError: 'NoneType' object does not support item assignment

Traceback (most recent call last): File "/usr/lib/python3/dist-packages/snappergui/changesWindow.py", line 145, in on_idle_init_paths_tree self.add_path_to_tree(str(entry[0]), int(entry[1]), files_tree) File "/usr/lib/python3/dist-packages/snappergui/changesWindow.py", line 70, in add_path_to_tree node.children[parts[-1]] = changesWindow.TreeNode(path, None, status, False)

TypeError: 'NoneType' object does not support item assignment 

[stelcodes]

Any update on this? I'm unable to view any diffs because of this bug.