INDIVIDUAL.GATHER.APPROACHING but idling

[elexis]

In this match with r22777, there were idle units in various instances that were standing in front of resources and in INDIVIDUAL.GATHER.APPROACHING state but not gathering nor trying to get to the resource.

[elexis]

In screenshot 655 there is similarly a unit standing in front of a building to build that it cant immediately reach and doesnt try a new path, but seems to have given up, if I'm not recollecting incorrectly without having changed the UnitAI state, because it IIRC continued to do something after the building was finished.

[Minohaka]

I don't know if units getting stuck in the forest, next to buildings, not capturing, not helping when constructing buildings is related to it. Often happens when units are carrying resources and you instruct a large group to build a new barracks for example (this one is maybe related to how many units are allowed to build at once)

[wraitii]

This might not be entirely fixed by ​Phab:D2239 (since replaying with the fix changes the state), but from the screenshots all issues seem similar (short distances stuckness in non-idle states), and the issue definitely exists. I'll leave this open for a while after committing that patch so that people can say if it still happens.

[wraitii]

In 22815:

Unit Motion - make sure units don't get stuck in the special long-path computation step.

In some rare cases, units could be stuck in the special state of 3 failed path computations, making them always compute long paths instead of trying short paths again. This can happen when they compute a long path successfully, but the unit cannot actually move as it gets obstructed right away.
Make sure this state is never kept for more than one turn to fix this problem.

Refs #5569 (probable fix but kept open for further investigating).

Differential Revision: ​https://code.wildfiregames.com/D2239

[wraitii]

Per the above, I assume this was fixed by rP22815 . Will re-open if necessary.