Main thread dispatch change (#1315) causes updateViewGroupOffline to hang

[ELeeScape]

I think #1315 broke updateViewGroupOffline and causes it to hang, because updateViewGroupOffline calls loadTiles and updateViewGroup in a loop until all tiles are loaded and those functions used to call _asyncSystem.dispatchMainThreadTasks() but now they don't, so loading never finishes. Or possibly I'm misunderstanding something?

[j9liu]

@ELeeScape you're absolutely right, thank you for the catch (and just in time for our releases)! Were you planning to open a quick PR for this fix?

[ELeeScape]

Sure, I can do that, though I'm still learning my way around cesium-native code base. Stand by.

[j9liu]

Thanks so @ELeeScape!

I also noticed we may have broken the (deprecated) Tileset::updateView for similar reasons, but the fix should be the same :')

cesium-native/Cesium3DTilesSelection/src/Tileset.cpp

Lines 373 to 378 in a543282

	const ViewUpdateResult&
	Tileset::updateView(const std::vector<ViewState>& frustums, float deltaTime) {
	const ViewUpdateResult& result =
	this->updateViewGroup(this->_defaultViewGroup, frustums, deltaTime);
	this->loadTiles();
	return result;