Philip Withnall authored Oct 17, 2023 and Philip Withnall committed Oct 22, 2023

When calling `g_file_set_contents_full()` without
`G_FILE_SET_CONTENTS_CONSISTENT`, the file is written by opening it,
`write()`ing to it, then closing it.

This is fine as long as the file is not longer than the new content you
want to set its contents to. If it is, the last bit of the old content
remains, because `g_file_set_contents_full()` was missing an
`ftruncate()` call.

Fix that, and change the tests to catch truncation failures in future.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Fixes: #3144

(Backport 2.78: Unmark new translatable string as translatable, to avoid
adding need for translations.)