Improve typing and handling of updateCheck state (#14739)
If the updateCheckState pickle is set to "None", the state fails to load correctly.
This can cause a crash.
It is uncertain as to the cause of the pickle being set to None, but it is assumed to do with exiting NVDA during initialization.
Description of user facing changes
Should fix rare crash where updateCheck.pickle is written to with invalid state information (unknown cause).
Description of development approach
Add typing, handle the case where pickle.load loads None for the state.
Testing strategy:
Set %appdata%/nvda/updateCheckState.pickle to "N." which loads as "None"
Test if NVDA crashes on start up
