If users click outside the search entry while it's empty we reset and
thus give up key focus. This means that when using an input method
with candidate popups, interacting with the popup with a mouse click
cancels the current input method context if there's no other text in
the entry besides the preedit string.
To avoid this we can check if the entry has preedit in addition to
checking if it has normal text.
https://bugzilla.gnome.org/show_bug.cgi?id=745167
b58f08bda1