Show internal name instead of crashing when buildable actor has no tooltip

But throw a lint error instead.

OpenRA.Mods.Common/Lint/CheckTooltips.cs

@@ -0,0 +1,35 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2016 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Linq;
+using OpenRA.Mods.Common.Traits;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Lint
+{
+	class CheckTooltips : ILintRulesPass
+	{
+		public void Run(Action<string> emitError, Action<string> emitWarning, Ruleset rules)
+		{
+			foreach (var actorInfo in rules.Actors)
+			{
+				var buildable = actorInfo.Value.TraitInfoOrDefault<BuildableInfo>();
+				if (buildable == null)
+					continue;
+
+				var tooltip = actorInfo.Value.TraitInfos<TooltipInfo>().FirstOrDefault(Exts.IsTraitEnabled);
+				if (tooltip == null)
+					emitError("The following buildable actor has no (enabled) Tooltip: " + actorInfo.Key);
+			}
+		}
+	}
+}