gstreamer: Do not call gst_deinit() but do free the device and effect manager objects on backend destruction.
gstreamer: Do not call gst_deinit() but do free the device and effect manager objects on backend destruction.

Integrated KDE change 1027566 by cguthrie.

Normally the backend is only destroyed once when the app exists, but calling gst_deinit()
means that the whole gstreamer system becomes unrecoverable. This means that if
you switch backends away from gstreamer and then back again it will not work.
Gstreamer devs recommend that you do not call gst_deinit() at all except in test cases.

Reviewed-by: Dmytro Poplavskiy
(cherry picked from commit 132ad441481e676cb4e502797c0a4fc833152175)

igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt