fix possible dereference of NULL pointer
Adapt to mate-desktop API changes

Based on gnome-settings-daemon commit 8fb7dd9c4dc6da34b4b2961c6212b91d6342152a
From: Giovanni Campagna <gcampagna@src.gnome.org>

MateRRScreen, MateRRConfig and MateRROutputInfo have been turned
into GObjects. Adapt to that.
Adapt to API changes in MateRRScreen

Based on gnome-settings-daemon commit: 3d4bb7d247ac1d70840cd7ea7247263d3f590d9f
From: Giovanni Campagna <gcampagna@src.gnome.org>

- mate_rr_screen_new has lost the callback parameter, replaced by "screen-changed" signal
- mate_rr_screen_destroy is gone
xrandr: Only connect to MateRRScreen's signal after checking it's not NULL

Taken from gnome-settings-deaemon commit:9b1fd55f4e65cad07a3f39de441aca53e34e7473
From: Rodrigo Moya <rodrigo@gnome-db.org>
XRandR plugin: cope with rename of get_active and get_connected

Now the methods are called is_active and is_connected

Based on gnome-settings-daemon commit: 68ff8cf63cea899b45d0ffb6950fdcc28d71fffd (patch)
From: Giovanni Campagna <gcampagna@src.gnome.org>
Connect to the right signal name

Based on gnome-settings-dameon commit: 107f7cdea4bcc508622e040d22e43a9e65574401
From: Emilio Pozuelo Monfort <pochu27@gmail.com>
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