Initial loading of default feeds are not available for offline reading

[nus-se-bot]

Describe the bug
The feeds that were added at load are not saved in the articles folder
To Reproduce
Steps to reproduce the behavior:

1. Turn off internet connection
2. Click on a feed
3. See error in display: The page cannot be displayed

Expected behavior
Since the articles are available for offline viewing, disconnecting the computer from the internet still allows us to view the articles. However the page cannot be displayed.

Screenshots

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Reported by: @jing1324
Severity: Low

_{[original: nus-cs2103-AY1819S2/pe-dry-run#939]}