python module: query_iter function must incref the query (problem surfaced because the query ref count is now correct following the previous incref fix

src/python/recoll/pyrecoll.cpp

@@ -861,6 +861,7 @@ Query_init(recoll_QueryObject *self, PyObject *, PyObject *)
 static PyObject *
 Query_iter(PyObject *self)
 {
+    Py_INCREF(self);
     return self;
 }