Fix segfault for empty iterators

This commit returns `false` if the first cell in `GetTableInfo` is NULL,
and relies on Python's exception handling of the error instead of
issuing a segfault.

src/params.cpp

@@ -967,6 +967,10 @@ static bool GetTableInfo(Cursor *cur, Py_ssize_t index, PyObject* param, ParamIn
     {
         PyObject *cell0 = PySequence_GetItem(param, 0);
         Py_XDECREF(cell0);
+        if (cell0 == NULL)
+        {
+            return false;
+        }
         if (PyBytes_Check(cell0) || PyUnicode_Check(cell0))
         {
             nskip++;