glib-2.0: fix rare GFileInfo test case failure

If a access or creation timestamp has 0 microseconds, then the test
fails as it doesn't expect this to be a valid value.  Expand a previous
fix for modification times to cover these timestamps too.

[ YOCTO #14373 ]

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>