No more focus event issue after reloading appModules (#17322)
Fixes #17323
Summary of the issue:
After a reload of plugins (`NVDA+control+f3`), focus events do not report the new focus as expected.
During focus event, NVDA tests which tree interceptors are alive or not to clean up those which are dead. In this test, for MSHTML, NVDA looks at `root.appModule.appName`, `root` being the root object associated to the virtual MSHTML buffer.
However, `root.appModule` may be `None` after plugins are reloaded.
Description of user facing changes
After plugins are reloaded while a browseable message is opened, the focus will no longer fail to be reported.
Description of development approach
Fixed the logic for MSHTML
Testing strategy:
Tested STR in #17323.
