UI issue during enemies turn probably related to reachmap

[gfgtdf]

during the enemies turn it often looks like this, to repdoruce it seems to be requires that you clicked one of your won units shortly before the enemies turn began.

[gfgtdf]

if you turn down accelerated sppeed really slow you can reproduce it better, you also need 'follow unit actions' activated: whiel the screen scrolls to the enemies leader the whole maps becomed covered with a reachmap overlay. (that doesn't disappear properly after the scrolling has finished)

[gfgtdf]

ok i looked a bit at the code and what i think i happening is:

1. The (ai) turn of side 2 starts, this changes the cursor at https://github.com/wesnoth/wesnoth/blob/1.13.10/src/playsingle_controller.cpp#L539

2. The user click on the map this sets display::reach_map_

3. during th ais turn the reach_map has no effect sicne it's blocked by https://github.com/wesnoth/wesnoth/blob/1.13.10/src/game_display.cpp#L278

4. When scrolling to side 3s leader, which happens "between" the turns, https://github.com/wesnoth/wesnoth/blob/1.13.10/src/game_display.cpp#L278 no longer blocks so the map is drawn with unreachable overlay on it.

5. back inside side 3's turn no hexes are invalidated since reach_map hasn't changed but tzhe overlay is not darwn for new hexes resuling in artifacts.

For now imm assignig tis to @AI0867 who made 38e9c55 which changes the appearanc of hexes ithout invalidating them. thi part coudl maybe be fixed by making all cursor changes call display::invalidate_all

But i also think that the fact that the reach map is shown while the map scrolls to the leader is somethign unexpected, and should be corrected.

[AI0867]

Okay, so I gather that the problem is that between AI turns, the reachmap is drawn, and then left there during the latter AI turn.

Looking at the original requirements in GNA #16350, depending on the cursor seems a bit of a hack. Also, the reachmap (among other things) should probably be cleared when we enter such a state.

[sevu]

I could reproduce this issue another way:
In TSG S4, when the first time a unit dies, a message is shown.
If I have this unit selected during the AI fighting it, it looks like this:

[sevu]

Can reproduce it with the fix and the above.

[sevu]

For the TSG test case: works best if I keep clicking the unit while the fight, until the [message] appears.