src/photos-searchbar.c: Changed ctrl+a behaviour in search

Currently while searching photos by text, hitting the Ctrl+a key will
select all photos that matched the query.

This can lead to unwanted behaviour, like searching for a term then
hitting Ctrl+a Backspace in order to change the query term; this
delete all found images.

To fix this, changed the search bar code for key pressing event in
order to select the text instead of the photos.

GNOME/gnome-photos#124
3 jobs for alter_ctrl_a_behaviour in 46 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #304013
flatpak

00:00:46

 
  Review
skipped #304014
review
skipped #304015
allowed to fail manual
stop_review
 
Name Stage Failure
failed
flatpak Test
Initialized empty Git repository in /builds/mcappadonna/gnome-photos/.flatpak-builder/git/https_gitlab.gnome.org_GNOME_gegl.git-020F2Z/
Fetching git repo https://gitlab.gnome.org/GNOME/gegl.git, ref refs/heads/master
From https://gitlab.gnome.org/GNOME/gegl
* [new branch] master -> master
Downloading http://exiv2.org/builds/exiv2-0.27.0-Source.tar.gz
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 100 334 100 334 0 0 1380 0 --:--:-- --:--:-- --:--:-- 1385
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
Failed to download sources: module exiv2: The requested URL returned error: 404 Not Found
ERROR: Job failed: exit code 1