[PATCH 2/4] Fix use-after-free warning with GCC at -O3

[Mike Hommey <mh@xxxxxxxxxxxx>]

```
reftable/basics.c: In function ‘parse_names’:
reftable/basics.c:233:17: error: pointer ‘names’ may be used after ‘free’ [-Werror=use-after-free]
  233 |                 reftable_free(names[i]);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~
In function ‘reftable_free’,
    inlined from ‘reftable_realloc’ at reftable/basics.c:30:3,
    inlined from ‘reftable_realloc’ at reftable/basics.c:27:7,
    inlined from ‘reftable_alloc_grow’ at reftable/basics.h:228:10,
    inlined from ‘parse_names’ at reftable/basics.c:214:8:
reftable/basics.c:44:17: note: call to ‘free’ here
   44 |                 free(p);
      |                 ^~~~~~~
```

Signed-off-by: Mike Hommey <mh@xxxxxxxxxxxx>
---
 reftable/basics.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/reftable/basics.c b/reftable/basics.c
index 9988ebd635..de21fe6ef7 100644
--- a/reftable/basics.c
+++ b/reftable/basics.c
@@ -229,9 +229,11 @@ char **parse_names(char *buf, int size)
 	return names;
 
 err:
-	for (size_t i = 0; i < names_len; i++)
-		reftable_free(names[i]);
-	reftable_free(names);
+	if (names) {
+		for (size_t i = 0; i < names_len; i++)
+			reftable_free(names[i]);
+		reftable_free(names);
+	}
 	return NULL;
 }
 
-- 
2.50.0.rc1.593.g042f21cb9b