No indication of what happened when IDE startup fails due to no Internet access

[PaszaVonPomiot]

Describe the bug
I'm posting this as bug because it could be considered as such by users.
When starting IDE while having firewall enabled Arduino gets stuck indefinitely without any error message and splash screen blocks central part of the screen.

To Reproduce
Steps to reproduce the behavior:

1. Have your firewall enabled (TinyWall in my case)
2. Start Arduino IDE
3. See the splash screen indefinitely
4. Close Arduino IDE
5. Open firewall traffic for Arduino IDE and CLI
6. Start Arduino IDE
7. See that it works

Expected behavior
Splash screen disappears and user can work in IDE
OR
Error message is displayed indicating no connection

Screenshots

Desktop (please complete the following information):

• OS: W10HOME
• Version: 2.0.0.beta4

[per1234]

Error message is displayed indicating no connection

This should already be the case when using the nightly build of Arduino IDE 2.x:
https://www.arduino.cc/en/software#nightly-builds

Thanks to #266, you should now get an informative error message when this happens, which will make it much easier to identify why the IDE was unable to fully start up.