Ensure Clear(T) also have a safety check to ensure no listener is attached.

Move related methods next to each other.
Change Clear(T) to use Array.Fill.

OpenRA.Game/Map/Map.cs

@@ -309,6 +309,7 @@ namespace OpenRA
 			Resources = new CellLayer<ResourceTile>(Grid.Type, size);
 			Height = new CellLayer<byte>(Grid.Type, size);
 			Ramp = new CellLayer<byte>(Grid.Type, size);
+			Tiles.Clear(terrainInfo.DefaultTerrainTile);
 			if (Grid.MaximumTerrainHeight > 0)
 			{
 				Height.CellEntryChanged += UpdateProjection;
@@ -316,8 +317,6 @@ namespace OpenRA
 				Tiles.CellEntryChanged += UpdateRamp;
 			}
 
-			Tiles.Clear(terrainInfo.DefaultTerrainTile);
-
 			PostInit();
 		}