Allow Outlook attachment list to read again

[michaelDCurran]

Link to issue number:

Fixes #12265

Summary of the issue:

After merging of pr #12210 , The attachment list in Outlook no longer read with NVDA, and an error was produced in the log.
It seems that Outlook's attachment list, gives back a NULL pointer for the SelectionContainer property on its UIA SelectionItemPattern.

Description of how this pull request fixes the issue:

Check to see if CurrentSelectionContainer is NULL and return None as there is nothing further we can do with that pattern.

Testing strategy:

• Ran steps to reproduce listed in nvda does not read the list of attachments in outlook  #12265 and verified that the Outlook attachment list reads again.
• Ensured that selections are still read in Microsoft Excel with UIA enabled, related to pr Optional experimental support for Microsoft Excel via UI Automation #12210.

Known issues with pull request:

None.

Change log entry:

None needed.

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[feerrenrut]

Looks good to me.