res_calendar: Plug memory leak and micro-optimization

ast_variables_destroy is NULL safe, so there is no need to check its
argument before passing it.

ASTERISK-25524 #close
Reported by: Jesper

Change-Id: Ib0f8057642e9d471960f1a79fd42e5a3ce587d3b

res/res_calendar.c

@@ -339,10 +339,7 @@ static void calendar_destructor(void *obj)
 	}
 	ast_calendar_clear_events(cal);
 	ast_string_field_free_memory(cal);
-	if (cal->vars) {
-		ast_variables_destroy(cal->vars);
-		cal->vars = NULL;
-	}
+	ast_variables_destroy(cal->vars);
 	ao2_ref(cal->events, -1);
 	ao2_unlock(cal);
 }

res/res_calendar_caldav.c

@@ -78,6 +78,7 @@ static void caldav_destructor(void *obj)
 	if (pvt->session) {
 		ne_session_destroy(pvt->session);
 	}
+	ne_uri_free(&pvt->uri);
 	ast_string_field_free_memory(pvt);
 
 	ao2_callback(pvt->events, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, NULL, NULL);