importing non existant url for feed stucks the feed import.

[gochev]

Describe the bug
I was trying to import my oldreader feeds OPML xml and it seems on raven reader it was stucking. The reason beeing some of the URLs are no longer available

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Import and Export' menu
2. Click on 'Import subscriptions'
3. Select the file :

https://gist.github.com/gochev/c06abb19215de2aef3a814f22817c536 (linking it like this since attachment of this file is not allowed.)

4. Observe it stucks

Expected behavior
to skip the non valid URLs or to show error or something

Screenshots
It just stucks on importing.
Desktop (please complete the following information):

• OS: Windows
• Browser Chrome but not related
• Version 1.0.79

Additional context
The two problematic URLs above are :
<outline type="rss" xmlUrl="http://java-bg.org/feed/"/>

since this domain doesnt exist and
<outline type="rss" xmlUrl="http://blogs.sun.com/theaquarium/feed/entries/atom"/>

basically same reason.

[stefonarch]

Probably the same here, impossible to import my opml file which works on all other feedreaders. Basically it blocks me from even trying Raven.