ViewFrame: select text in the search entry

Steps:
- Ctrl+F and search for 'something', with a least one match
- the match becomes selected in the buffer
- press Enter to quit the search
- press Ctrl+F again
- the search takes the buffer selection to put it in the search entry

What the code did in this case is to put the cursor at the end of the
search text (in the search entry). Now it selects the text.

https://bugzilla.gnome.org/show_bug.cgi?id=723267