fix(developer): compiler crash when no project loaded

Fixes #9889.

This arises from a deprecated way of using Keyman Developer by starting
Keyman Developer by opening a keyboard .kmn file from Explorer, which
causes Developer to run in a 'projectless' mode. This was not tested in
the new compiler integration, and that has caused this crash.

In 'projectless' mode, there is still a global 'untitled' project, but
the files loaded do not 'belong' to it. The compiler settings are
inherited from the global 'untitled' project in this case.