The Add-on Store no longer fails to reopen after an add-on installation and before NVDA restart (#19901)
Fixes #19900
### Summary of the issue:
After an add-on had been installed and the Store closed, the Store could
not be reopened until NVDA was restarted.
### Description of user facing changes:
The Add-on Store can now be reopened after an add-on has been installed,
even before NVDA has been restarted.
For add-ons pending install, the install date is not provided since the
installation is completed after NVDA has restarted.
Add-ons without install date are sorted after all other add-ons.
### Description of developer facing changes:
`addonStore.models.addon._AddonManifestModel.installDate` may now be `None`.
### Description of development approach:
* `_AddonManifestModel.installDate` now returns `None` if the add-on is
not completely installed; take this into account when using this value.
* If the `installDate` is `None`, use `datetime.max` to sort the add-on
after all other ones.
### Testing strategy:
Manual tests:
* Tested #19900 STR and checked details field and install date column.
* Sorted add-ons by install date column in the list.
### Known issues with pull request:
Non
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Co-authored-by: Cyrille Bougot <cyrille.bougot@laposte.net>