Automatically check for updates after regaining an Internet connection

[cassidyjames]

Now that we support browsing offline in AppCenter, you can get into a weird state:

1. Open AppCenter with no Internet connection
2. Get an error about not being able to fetch updates (#1156)
3. Ignore it
4. Reconnect to the Internet

Instead of checking for updates when regaining an Internet connection, you're stuck without updates as if you're still offline.

[davidmhewitt]

I spotted code that's supposed to handle this already: https://github.com/elementary/appcenter/blob/9165da251bcde7963c6b0895ffcf005d5bf5627f/src/Application.vala#L152-L154

Do we know for sure it doesn't already work?

[cassidyjames]

@davidmhewitt I mean, in master I can reliable reproduce this:

• Ensure there are some outstanding updates
• Log in with network disconnected (or kill AppCenter, disconnect network, and start AppCenter again)
• Reconnect network
• See the infobar go away
• No updates ever appear, and the homepage never updates

If I restart AppCenter with the network connected, the homepage loads correctly and updates appear again.

[danirabbit]

Fixed in #2314