Increase ref-count as documented for PyErr_Restore

Author: filmor

src/runtime/exceptions.cs

@@ -269,6 +269,9 @@ public static void SetError(Exception e)
             PythonException pe = e as PythonException;
             if (pe != null)
             {
+                Runtime.XIncref(pe.PyType);
+                Runtime.XIncref(pe.PyValue);
+                Runtime.XIncref(pe.PyTB);
                 Runtime.PyErr_Restore(pe.PyType, pe.PyValue, pe.PyTB);
                 return;
             }