Only lazy load on reload

[davidism]

The default behavior of the flask run command is to lazily import the application if the reloader is enabled. This prevents syntax errors from crashing the app on reload, but it also means that such errors are deferred until the first request.

If the reloader is enabled, use eager loading the first time to show errors immediately. This way, initial errors will be shown to the user when they run the command, but errors introduced later will not crash the server.