On Locomotor initialization, update blocked cells.

Prior to ef44c31a72eab61a597cf539ee4b138e94b254fe, Locomotor would be earlier in the trait initialization sequence than SpawnMapActors. Locomotor would assume no actors on the map, and register to update blocked cells when new ones were added. When SpawnMapActors created actors, Locomotor was made aware and kept up-to-date.

After this commit, the initialization sequence was perturbed and SpawnMapActors would initialize first. Locomotor would assume no actors on the map and thus be unaware of these starting units, meaning those starting units would not cause blocking, allowing units to pass through them.

There are two possible fixes. SpawnMapActorsInfo can initialize NotBefore<LocomotorInfo>, enforcing that actors are spawned after locomotor is ready. Or we can remove the assumption in Locomotor that the map starts empty, and have it update blocked cells on startup. The latter seems cleaner, so any other traits that may want to spawn actors don't have to be aware sequencing their initialization with the Locomotor trait, instead things would "just work".

OpenRA.Mods.Common/Traits/World/Locomotor.cs

@@ -365,16 +365,18 @@ namespace OpenRA.Mods.Common.Traits
 		{
 			var map = w.Map;
 			actorMap = w.ActorMap;
+			map.CustomTerrain.CellEntryChanged += UpdateCellCost;
+			map.Tiles.CellEntryChanged += UpdateCellCost;
 			actorMap.CellUpdated += CellUpdated;
 
 			cellsCost = new[] { new CellLayer<short>(map) };
 			blockingCache = new[] { new CellLayer<CellCache>(map) };
 
 			foreach (var cell in map.AllCells)
+			{
 				UpdateCellCost(cell);
-
-			map.CustomTerrain.CellEntryChanged += UpdateCellCost;
-			map.Tiles.CellEntryChanged += UpdateCellCost;
+				UpdateCellBlocking(cell);
+			}
 
 			// NotBefore<> ensures all custom movement layers have been initialized.
 			var customMovementLayers = world.GetCustomMovementLayers();