Fix uninitialized struct member (GH-19589)

diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
index 78706b6..fd4b4c2 100644
--- a/Modules/_functoolsmodule.c
+++ b/Modules/_functoolsmodule.c
@@ -1195,6 +1195,7 @@
     obj->maxsize = maxsize;
     Py_INCREF(cache_info_type);
     obj->cache_info_type = cache_info_type;
+    obj->dict = NULL;
     return (PyObject *)obj;
 }