feat(developer): Installation doesn't show "finished" screen after reboot

**Describe the bug**
If a user's system requires a reboot to fully install Keyman Developer, the post-reboot sequence of events doesn't indicate when the installation is complete.

**To Reproduce**
Steps to reproduce the behavior:
1. Have an older version of Keyman Developer installed
a. If not previously installed, do so.
b. If you just installed Developer the first time, reboot your computer (so that installed Developer dependencies will be loaded by the system)
2. Install the current version (12.0.50.0) of Keyman Developer. This should trigger a "system reboot required" since some files will have been in use.
3. When the installer requests the reboot, click "OK" and let the system reboot.
4. ...
5. Once you log in to Windows post-reboot, a few seconds later the installer should auto-launch. The screen shown will appear to be the installer's initial screen.
6. Tell it to install, checking for updates.
7. [The bug] Watch as the installer simply disappears once the update-check (quickly) completes. It's actually done now (or quite shortly from now), but no more UI will be displayed.

**Expected behavior**
I'd expect to see a screen saying "Keyman Developer 12.0 installed successfully!" with an option to launch on the screen's close. You know, standard 'finished installer' stuff.

**Environment**
OS: Windows 10 (Version 1903, build 18362.388)
Product: Keyman Developer 12.0.50.0 (the first stable release)