Backport r56875 from py3k; double LEAVE_PYTHON when AsString() fails
in PythonCmd().
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index 07570f3..d26728c 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -2028,7 +2028,9 @@
 
 	s = AsString(res, tmp);
 	if (s == NULL) {
-		rv = PythonCmd_Error(interp);
+		Py_DECREF(res);
+		Py_DECREF(tmp);
+		return PythonCmd_Error(interp);
 	}
 	else {
 		Tcl_SetResult(Tkapp_Interp(self), s, TCL_VOLATILE);