Fix keyboard navigation in the search results, bnc#863950

This fix is ported from gnome-control-center upstream:
https://github.com/GNOME/gnome-control-center/commit/48e6fd296708e04953ca62b8a1886ce47999f628
Merge pull request #10 from FelixZhang/bnc#863950

Fix keyboard navigation in the search results, bnc#863950