(cherry picked from commit fb927d964bace3f7e5351ef52d04cdd1ba21eb03)

(cherry picked from commit 9c32fe258a5e6494cd2a7a53ee3cc1a5d2825cc6)

Also add a file selection test to the test suite to ensure this and
other functionality is working properly.

Fixes: #80

filesel: Allow a non-existing filename with --save

Closes #80

See merge request GNOME/zenity!40

Fixes: #82

Technically this is private API, but STDIN influences the calling of
this API, so more checks should be inserted.

Related: #82

(cherry picked from commit 537d14d38e9c9722dc017bddb7487ceec0a4c2a3)

colview: Return if nth item of row exceeds num items in row

Closes #82

See merge request GNOME/zenity!42

(cherry picked from commit c96d917cab02e9fce603d80e60ea088284aec1fd)

(cherry picked from commit 1f4bdf8ccff80a2a61783f88557f4069db972654)

This emulates the behaviour of zenity3. Although this was not documented
in zenity3, this was pretty clearly stipulated in the zenity3 source
code and may be expected behaviour for zenity 3->4 migration.

Fixes: #85

Fixes: #86

(cherry picked from commit f4da05d66043d2db9a36c42e00166f8e9cc06c7a)

Closes: https://gitlab.gnome.org/GNOME/zenity/-/issues/91

main: Fix command-line signal signature

Closes #91

See merge request GNOME/zenity!46

colview: Clicking on column titles should sort items

Closes #86

See merge request GNOME/zenity!44

Fixes: #90