Errors during route preloading are not handled

[th0r]

The logic that initiates preloading of a lazy route doesn't handle potential load errors (e.g. bad network connection) so they are thrown. I think preloader should ignore them as they're not critical but we have to ensure they don't break the app and router will initiate loading of the failed module after user navigates to the corresponding route.

Here is the stacktrace of one of such errors:

[th0r]

@mgechev sorry, did you have time to take a look at this?