polish multiple rows of pips (RA proc)

OpenRA.Game/Traits/Selectable.cs

@@ -109,7 +109,11 @@ namespace OpenRA.Traits
 
 			foreach (var pips in self.TraitsImplementing<IPips>())
 			{
-				foreach (var pip in pips.GetPips(self))
+				var thisRow = pips.GetPips(self);
+				if (thisRow == null)
+					continue;
+
+				foreach (var pip in thisRow)
 				{
 					if (pipxyOffset.X+5 > self.GetBounds(false).Width)
 					{

OpenRA.Mods.RA/OreRefinery.cs

@@ -125,7 +125,7 @@ namespace OpenRA.Mods.RA
 		public IEnumerable<PipType> GetPips (Actor self)
 		{
 			if (!Info.LocalStorage)
-				return new PipType[] { };
+				return null;
 			
 			return Graphics.Util.MakeArray (Info.PipCount, i => (Ore * 1f / Info.Capacity > i * 1f / Info.PipCount) ? Info.PipColor : PipType.Transparent);
 		}