Use static empty pathfinding path when possible

OpenRA.Mods.RA/Move/PathFinder.cs

@@ -25,6 +25,8 @@ namespace OpenRA.Mods.RA.Move
 
 	public class PathFinder
 	{
+		readonly static List<CPos> emptyPath = new List<CPos>(0);
+
 		readonly World world;
 		public PathFinder(World world) { this.world = world; }
 
@@ -50,7 +52,7 @@ namespace OpenRA.Mods.RA.Move
 					Log.Write("debug", "Actor {0} asked for a path from {1} tick(s) ago", self.ActorID, world.FrameNumber - cached.tick);
 					if (world.FrameNumber - cached.tick > MaxPathAge)
 						CachedPaths.Remove(cached);
-					return new List<CPos>(cached.result);
+					return emptyPath;
 				}
 
 				var mi = self.Info.Traits.Get<MobileInfo>();
@@ -61,7 +63,7 @@ namespace OpenRA.Mods.RA.Move
 				{
 					var passable = mi.GetMovementClass(world.TileSet);
 					if (!domainIndex.IsPassable(from, target, (uint)passable))
-						return new List<CPos>(0);
+						return emptyPath;
 				}
 
 				var pb = FindBidiPath(
@@ -103,7 +105,7 @@ namespace OpenRA.Mods.RA.Move
 					var passable = mi.GetMovementClass(world.TileSet);
 					tilesInRange = new List<CPos>(tilesInRange.Where(t => domainIndex.IsPassable(src, t, (uint)passable)));
 					if (tilesInRange.Count() == 0)
-						return new List<CPos>(0);
+						return emptyPath;
 				}
 
 				var path = FindBidiPath(
@@ -144,7 +146,7 @@ namespace OpenRA.Mods.RA.Move
 				}
 
 				// no path exists
-				return new List<CPos>(0);
+				return emptyPath;
 			}
 		}
 
@@ -209,7 +211,7 @@ namespace OpenRA.Mods.RA.Move
 						return path;
 				}
 
-				return new List<CPos>(0);
+				return emptyPath;
 			}
 		}