Invalid/empty HTTPS private or certificate key causes web server to break

[ITAC85v2]

Edit: I think I accidentally wrote a duplicate issue, not sure if I should close or not.

I stumbled upon this accidentally when I tried to enable HTTPS but forgot to generate the keys. I'm using Chrome OS, by the way, if that's helpful at all.

What happens is it at first shows URI as https://(ip):undefined/

Then upon restarting the web server, it refuses to start, even after restarting the app (the only way to fix it is to kill the app)

Here's the steps to reproduce:
-Start the web server
-Enable "Use https://"
-Set "Private key string" and "Certificate string" to empty or something invalid
(url should now show https://(ip):undefined, even after disabling https)
-Stop and start the web server
(the web server should now refuse to start and forever say "starting")

It's not a huge issue, but it did cause me a little bit of headache when I found it, trying to get the web server to work again.

[ethanaobrien]

#264 will fix this