fix(windows): avoid error if keyman32.dll renamed

Fixes #4939.
Fixes KEYMAN-WINDOWS-70.
Fixes KEYMAN-WINDOWS-71.
Fixes KEYMAN-WINDOWS-BR.
Fixes KEYMAN-WINDOWS-6J.

I am speculating a little here, because the root cause is not visible in
the crash report, but it appears that if keyman32.dll is renamed, that
the UnregisterControllerWindows function attempts to reload keyman32.dll
which means that (a) it no longer has a list of registered controllers,
and (b) it may fail to reload.

Instead of throwing an exception, we now only log this error in
development mode. The error is not likely to cause significant trouble
for end users as they are shutting down Keyman anyway at this point.

The resolution if there is any uncertainty during an upgrade is to
restart Windows. This is less than ideal but avoids file locks and
problems with in-memory DLLs. (Future versions of Keyman will schedule
upgrades to happen automatically after a restart before Keyman has been
started, in an effort to avoid this kind of trauma.)