Moved setting otr.warn -> enc.warn

tests/unittests/ui/stub_ui.c

@@ -447,6 +447,7 @@ void cons_roster_setting(void) {}
 void cons_presence_setting(void) {}
 void cons_wrap_setting(void) {}
 void cons_winstidy_setting(void) {}
+void cons_encwarn_setting(void) {}
 void cons_time_setting(void) {}
 void cons_mouse_setting(void) {}
 void cons_statuses_setting(void) {}