Fix SystemError when nested function has annotation on positional-only argument (GH-17826)

(cherry picked from commit ec007cb43faf5f33d06efbc28152c7fdcb2edb9c)

Co-authored-by: Anthony Sottile <asottile@umich.edu>
diff --git a/Python/symtable.c b/Python/symtable.c
index b871358..30482d9 100644
--- a/Python/symtable.c
+++ b/Python/symtable.c
@@ -1717,6 +1717,8 @@
 symtable_visit_annotations(struct symtable *st, stmt_ty s,
                            arguments_ty a, expr_ty returns)
 {
+    if (a->posonlyargs && !symtable_visit_argannotations(st, a->posonlyargs))
+        return 0;
     if (a->args && !symtable_visit_argannotations(st, a->args))
         return 0;
     if (a->vararg && a->vararg->annotation)