fix: update error message for negative nelements in readline_append_history_file_impl

Author: cla7aye15I4nd

Modules/readline.c

@@ -391,7 +391,7 @@ readline_append_history_file_impl(PyObject *module, int nelements,
 {
     if (nelements < 0)
     {
-        PyErr_SetString(PyExc_ValueError, "nelements must be positive");
+        PyErr_SetString(PyExc_ValueError, "nelements must be non-negative");
         return NULL;
     }