Call TriggerOverrideEligibleStartingRegion with self

[copyrite]

Fixes #1529

[copyrite]

Ran a test where I had the following in a for-loop inside XComGameState_HeadquartersXCom.SetUpHeadquarters:

class'XComGameState_RegionLink'.static.CreateAllLinks(StartState);
class'XComGameState_RegionLink'.static.RandomizeLinks(StartState);

//Pick which region the HQ will start in
foreach StartState.IterateByClassType(class'XComGameState_WorldRegion', IterateRegion)
{
	if (default.PossibleStartingRegions.Find(IterateRegion.GetMyTemplateName()) != INDEX_NONE)
	{
		AllStartingRegions.AddItem(IterateRegion);
	}

	// Try to find an optimal starting region
	if(IterateRegion.CanBeStartingRegion(StartState))
	{
		BestStartingRegions.AddItem(IterateRegion);
	}
}
if(BestStartingRegions.Length > 0)
{
	RandomIndex = `SYNC_RAND_STATIC(BestStartingRegions.Length);
	BaseRegion = BestStartingRegions[RandomIndex];
}
else
{
	RandomIndex = `SYNC_RAND_STATIC(AllStartingRegions.Length);
	BaseRegion = AllStartingRegions[RandomIndex];
}
`Log("BaseRegion is" @ string(BaseRegion.m_TemplateName));

Additionally, an event listener that returned true only for Eastern Europe, false for others. Also an event listener that allowed non-continent links, but I'm not sure if that was necessary.

Without the fix, BaseRegion was always Eastern Europe's neighboring region; with the fix, 100% of the time Eastern Europe. I think that's more than enough confirmation that the fix is effective.