Fix exception handling for PDT operator.

Assets/Cryville/Common/Pdt/PdtOperator.cs

@@ -47,12 +47,12 @@ namespace Cryville.Common.Pdt {
 		internal void Call(byte* prmem, bool noset) {
 			_prmem = prmem;
 			_rfreq = false;
-			Execute();
-			if (!_rfreq && !noset) throw new InvalidOperationException("Return frame not set");
+			try { Execute(); } catch (Exception) { _failure = true; }
 			if (_failure) {
 				if (_rfreq) _etor.DiscardStack();
 				throw new InvalidOperationException("Evaluation failed");
 			}
+			if (!_rfreq && !noset) throw new InvalidOperationException("Return frame not set");
 		}
 		/// <summary>
 		/// Executes the operator.