Application not properly unregister in voicemail

(closes issue #18128)
Reported by: junky
Patches: 
      vm_unregister.diff uploaded by junky (license 177)
Tested by: pabelanger, lmadsen


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@292436 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -12541,6 +12541,7 @@ static int unload_module(void)
 	res |= ast_unregister_application(app2);
 	res |= ast_unregister_application(app3);
 	res |= ast_unregister_application(app4);
+	res |= ast_unregister_application(sayname_app);
 	res |= ast_custom_function_unregister(&mailbox_exists_acf);
 	res |= ast_manager_unregister("VoicemailUsersList");
 	res |= ast_data_unregister(NULL);