Fix the bug of reloader with windows path

[frostming]

Fix #1614

The root cause is that when running as flask run the value of __main__.__package__ is "". Modify the condition a little to make it fix the first branch.

Tested python app.py, flask run, python -m flask run on both Windows and WSL Ubuntu. All work fine. I have not got a PyDev running for testing, and it would be great if someone can help, but I think it should work with little risk.

[davidism]

Unfortunately, this kind of does the wrong thing the other direction. If you do python -m example to run a local module example.py, __package__ is the empty string, but it should be going into the else block since it's run as a module. It still works, but for the wrong reason.

According to sources I found when originally working on the reloader, __main__.__package__ is None indicates that we are running as a module, the empty string has a different meaning. https://stackoverflow.com/q/21233229/400617

[davidism]

Thanks for getting this started! I changed the check to be very specific to "looks like a misbehaving Windows entry point" so that it wouldn't interfere with other use cases.