Fix exception handling on failure to get operator.

Assets/Cryville/Common/Pdt/PdtEvaluatorBase.cs

@@ -157,7 +157,11 @@ namespace Cryville.Common.Pdt {
 		internal void Operate(PdtOperatorSignature sig) {
 			PdtOperator op;
 			try { op = GetOperator(sig); }
-			catch (Exception) { _framecount -= sig.ParamCount; return; }
+			catch (Exception) {
+				for (int i = 0; i < sig.ParamCount; i++)
+					DiscardStack();
+				throw;
+			}
 			Operate(op, sig.ParamCount);
 		}
 		/// <summary>