net: Check if returned pointer for allocated memory is NULL

When using grub_malloc(), the function can fail if we are out of memory.
After allocating memory we should check if this function returned NULL
and handle this error if it did.

Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/net/net.c

@@ -227,6 +227,11 @@ grub_net_ipv6_get_slaac (struct grub_net_card *card,
     }
 
   slaac->name = grub_malloc (sz);
+  if (slaac->name == NULL)
+    {
+      grub_free (slaac);
+      return NULL;
+    }
   ptr = grub_stpcpy (slaac->name, card->name);
   if (grub_net_hwaddr_cmp (&card->default_address, hwaddr) != 0)
     {