battstat: fix deprecated up_client_get_devices

[raveit65]

The previous code would have leaked all the UpDevice objects because no
free function was set on the returned GPtrArray.

With depending on upower-glib 0.99.8 get_devices() was deprecated and get_devices2() was introduced, we
can simply switch to get_devices2() which does set a free function on
the returned GPtrArray, stopping the leak.

[rbuj]

I think that we can also bump upower to 0.99.8 and remove legacy code.

mate-applets/configure.ac

Line 21 in 01e8f8a

UPOWER_REQUIRED=0.9.4

[raveit65]

You're right, done.

[rbuj]

Test:

$ CFLAGS="-fsanitize=leak -fno-omit-frame-pointer -g -ggdb3 -O0" LDFLAGS="-fsanitize=leak -ggdb3" ./autogen.sh --prefix=/usr && make && sudo make install

[raveit65]

Origin comment was taken from mate-desktop/mate-power-manager@9d5b257
which was from
https://gitlab.gnome.org/GNOME/gnome-control-center/commit/c1210c5
https://gitlab.freedesktop.org/upower/upower/commit/cb1071b

I think it is more a leak in upower itself.

[rbuj]

Using a global variable makes more sense like in #443, since the list of devices is updated dynamically and specific events are triggered.

[raveit65]

I only wanted to fix the deprecation. Any improvements can be done in another PR.
And it has a significant improvement from your previous post:
Before:
SUMMARY: LeakSanitizer: 21220 byte(s) leaked in 725 allocation(s).
After:
SUMMARY: LeakSanitizer: 20143 byte(s) leaked in 709 allocation(s).