Improve robustness of editor actor cell checks.

OpenRA.Mods.Cnc/Traits/Render/WithBuildingBib.cs

@@ -58,9 +58,15 @@ namespace OpenRA.Mods.Cnc.Traits
 				var cell = location + cellOffset;
 
 				// Some mods may define terrain-specific bibs
+				var sequence = Sequence;
+				if (map.Tiles.Contains(cell))
+				{
 					var terrain = map.GetTerrainInfo(cell).Type;
 					var testSequence = Sequence + "-" + terrain;
-				var sequence = anim.HasSequence(testSequence) ? testSequence : Sequence;
+					if (anim.HasSequence(testSequence))
+						sequence = testSequence;
+				}
+
 				anim.PlayFetchIndex(sequence, () => index);
 				anim.IsDecoration = true;
 

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

@@ -263,8 +263,16 @@ namespace OpenRA.Mods.Common.Traits
 				return map.Grid.DefaultSubCell;
 
 			for (var i = (byte)SubCell.First; i < map.Grid.SubCellOffsets.Length; i++)
-				if (!previews.Any(p => p.Footprint[cell] == (SubCell)i))
+			{
+				var blocked = previews.Any(p =>
+				{
+					SubCell s;
+					return p.Footprint.TryGetValue(cell, out s) && s == (SubCell)i;
+				});
+
+				if (!blocked)
 					return (SubCell)i;
+			}
 
 			return SubCell.Invalid;
 		}