[2.7] bpo-34457: Python/ast.c: Add missing NULL check to...

[2.7] bpo-34457: Python/ast.c: Add missing NULL check to alias_for_import_name(). (GH-8852) (GH-8858)

Reported by Svace static analyzer.
(cherry picked from commit 28853a24)
Co-authored-by: Alexey Izbyshev <izbyshev@ispras.ru>

Python/ast.c

@@ -2520,6 +2520,8 @@ alias_for_import_name(struct compiling *c, const node *n, int store)
             break;
         case STAR:
             str = PyString_InternFromString("*");
+            if (!str)
+                return NULL;
             PyArena_AddPyObject(c->c_arena, str);
             return alias(str, NULL, c->c_arena);
         default: