Check that suggestion candidates in calculate_suggestions are strings.

Author: devdanzin

Python/suggestions.c

@@ -148,6 +148,10 @@ _Py_CalculateSuggestions(PyObject *dir,
     }
     for (Py_ssize_t i = 0; i < dir_size; ++i) {
         PyObject *item = PyList_GET_ITEM(dir, i);
+        if (!PyUnicode_Check(item)) {
+            PyMem_Free(buffer);
+            return NULL;
+        }
         if (_PyUnicode_Equal(name, item)) {
             continue;
         }