Support observing with newer version

[ProditorMagnus]

Functional requirements:

• [ ] when version X is hosted, version X+1 can observe
• [x] when version X is hosted, version X+1 cannot join
• [x] when version X is hosted, version X-1 cannot join or observe, and is made to update
• [x] when version X is hosted, version X can join and observe
• [x] when version X is hosted, missing addon cannot join or observe

[ProditorMagnus]

Workaround

diff --git a/src/game_initialization/lobby_data.cpp b/src/game_initialization/lobby_data.cpp
index 9bf2866..0d249ea 100644
--- a/src/game_initialization/lobby_data.cpp
+++ b/src/game_initialization/lobby_data.cpp
@@ -510,7 +510,8 @@ game_info::ADDON_REQ game_info::check_addon_version_compatibility(const config&
                        });

                        required_addons.push_back(r);
-                       return r.outcome;
+                       return SATISFIED;
+                       // return r.outcome;
                }

                // Check if our version is too out of date to play.

Functional requirements state with this change:

• [x] when version X is hosted, version X+1 can observe
• [ ] when version X is hosted, version X+1 cannot join
• [x] when version X is hosted, version X-1 cannot join or observe, and is made to update
• [x] when version X is hosted, version X can join and observe
• [x] when version X is hosted, missing addon cannot join or observe

[ProditorMagnus]

https://github.com/wesnoth/wesnoth/issues/4358#issuecomment-535214375

[ProditorMagnus]

Requires testing how it behaves it normal clients.

[ProditorMagnus]

Nothing that can be done within addon code.