Fix memory leak

[alxvmr]

Hello! 👋
When running dconf update, a large memory leak was detected:

[root@lenovo-93812 RPMS.hasher]# ps aux | grep mate-menu
aleksee+   48198  2.0  0.6 918548 106816 ?       Sl   11:17   0:01 mate-menu
root       48280  0.0  0.0   6064  2220 pts/1    S+   11:19   0:00 grep --color=auto mate-menu
[root@lenovo-93812 RPMS.hasher]# ps up 48198
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   48198  2.0  0.6 918548 106816 ?       Sl   11:17   0:01 mate-menu
[root@lenovo-93812 RPMS.hasher]# dconf update
[root@lenovo-93812 RPMS.hasher]# ps up 48198
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   48198 11.8  0.9 938980 151908 ?       Sl   11:17   0:12 mate-menu
[root@lenovo-93812 RPMS.hasher]# dconf update
[root@lenovo-93812 RPMS.hasher]# dconf update
[root@lenovo-93812 RPMS.hasher]# dconf update
[root@lenovo-93812 RPMS.hasher]# ps up 48198
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   48198 31.9  1.4 1039960 234804 ?      Rl   11:17   0:40 mate-menu

The problem was that the application plugin was not releasing memory when regenerating due to references.

The attached commit fixes the situation - the application plugin is released from memory and the associated leak goes away.

root@lenovo-93812 ~]# ps aux | grep mate-menu
aleksee+   49326  5.8  0.5 824756 91060 ?        Sl   11:27   0:00 mate-menu
root       49345  0.0  0.0   6064  2108 pts/2    S+   11:27   0:00 grep --color=auto mate-menu
[root@lenovo-93812 ~]# ps up 49326
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   49326  4.0  0.5 824756 91068 ?        Sl   11:27   0:00 mate-menu
[root@lenovo-93812 ~]# dconf update
[root@lenovo-93812 ~]# ps up 49326
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   49326 10.5  0.7 912540 119600 ?       Sl   11:27   0:06 mate-menu
[root@lenovo-93812 ~]# dconf update
[root@lenovo-93812 ~]# dconf update
[root@lenovo-93812 ~]# dconf update
[root@lenovo-93812 ~]# ps up 49326
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
aleksee+   49326 33.6  0.9 918580 150544 ?       Sl   11:27   0:36 mate-menu