Fix logged error when locking up the computer

[CyrilleB79]

Hi Woody

Here is a PR fixing a a little issue; there is no functional issue though.

Issue

When locking the computer (Windows+l)or switching to a secure screen, an error message is logged:

ERROR - NVDAObjects.__call__ (11:30:31.558) - MainThread (8364):
Exception in chooseNVDAObjectOverlayClasses for GlobalPlugin ('globalPlugins.Access8Math')
Traceback (most recent call last):
  File "NVDAObjects\__init__.pyc", line 118, in __call__
  File "C:\Users\Cyrille\AppData\Roaming\nvda\addons\Access8Math\globalPlugins\Access8Math\__init__.py", line 204, in chooseNVDAObjectOverlayClasses
    if obj.windowClassName == "wxWindowNR" and obj.role == ROLE_WINDOW and obj.name == _("Access8Math interaction window"):
       ^^^^^^^^^^^^^^^^^^^
AttributeError: '_SecureDesktopNVDAObject' object has no attribute 'windowClassName'

The error is due to the fact that not all NVDAObject's are Window objects and thus, not all have a windowClassName attribute. More specifically, the secure screen object is not an object corresponding to a real window.

This error does not cause functional issue but having error that should be ignored in the log is disturbing when performing other debug tasks.

Solution

Try to get the windowClassName attribute and return None if it is missing.