Fix pull to refresh. See rest of message for repro steps.
Fix pull to refresh. See rest of message for repro steps.

Fixes the following bug:

On app clean start:

On iOS 10.3.1:
- tap "Saved" tab bar icon
- do pull to refresh on "All articles"
- tap "Reading lists"
- do pull to refresh
- switch back to "All articles"
- attempt pull to refresh again, which won't work

On iOS 11.2:
- tap "Saved" tab bar icon
- do pull to refresh on "All articles"
- tap "Reading lists"
- do pull to refresh, which won't work

josve05a/wikipedia-ios,julienbodet/wikipedia-ios,wikimedia/wikipedia-ios,wikimedia/apps-ios-wikipedia,wikimedia/apps-ios-wikipedia,montehurd/apps-ios-wikipedia,julienbodet/wikipedia-ios,josve05a/wikipedia-ios,wikimedia/apps-ios-wikipedia,josve05a/wikipedia-ios,montehurd/apps-ios-wikipedia,wikimedia/apps-ios-wikipedia,montehurd/apps-ios-wikipedia,julienbodet/wikipedia-ios,josve05a/wikipedia-ios,wikimedia/wikipedia-ios,julienbodet/wikipedia-ios,montehurd/apps-ios-wikipedia,wikimedia/apps-ios-wikipedia,julienbodet/wikipedia-ios,montehurd/apps-ios-wikipedia,wikimedia/wikipedia-ios,montehurd/apps-ios-wikipedia,montehurd/apps-ios-wikipedia,montehurd/apps-ios-wikipedia,wikimedia/wikipedia-ios,wikimedia/apps-ios-wikipedia,josve05a/wikipedia-ios,wikimedia/wikipedia-ios,wikimedia/wikipedia-ios,julienbodet/wikipedia-ios,josve05a/wikipedia-ios,julienbodet/wikipedia-ios,josve05a/wikipedia-ios,wikimedia/apps-ios-wikipedia,wikimedia/wikipedia-ios,josve05a/wikipedia-ios,julienbodet/wikipedia-ios,wikimedia/apps-ios-wikipedia