zebra: Fix compilation warning

Make sure the variable `srv6` is not NULL before dereferencing it.

Fixes the following compilation warnings:

```
error	15-Aug-2024 14:20:01	zebra/zebra_srv6_vty.c:974:8: warning: Access to field 'locators' results in a dereference of a null pointer (loaded from variable 'srv6') [core.NullDereference]
error	15-Aug-2024 14:20:01	                for (ALL_LIST_ELEMENTS_RO(srv6->locators, node, locator)) {
error	15-Aug-2024 14:20:01	                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error	15-Aug-2024 14:20:01	./lib/linklist.h:345:11: note: expanded from macro 'ALL_LIST_ELEMENTS_RO'
error	15-Aug-2024 14:20:01	        (node) = listhead(list), ((data) = NULL);                              \
error	15-Aug-2024 14:20:01	                 ^~~~~~~~~~~~~~
error	15-Aug-2024 14:20:01	./lib/linklist.h:63:22: note: expanded from macro 'listhead'
error	15-Aug-2024 14:20:01	#define listhead(X) ((X) ? ((X)->head) : NULL)
error	15-Aug-2024 14:20:01	                     ^
```

Signed-off-by: Carmine Scarpitta <cscarpit@cisco.com>

diff --git a/zebra/zebra_srv6_vty.c b/zebra/zebra_srv6_vty.c
index c664a9c69f1ef758256223666427ef7dadd81f40..5a80524149027b6ac91f0fa51672780a09a98c06 100644 (file)
--- a/zebra/zebra_srv6_vty.c
+++ b/zebra/zebra_srv6_vty.c
@@ -969,7 +969,7 @@ static int zebra_sr_config(struct vty *vty)
                                &srv6->encap_src_addr);
                }
        }
-       if (zebra_srv6_is_enable()) {
+       if (srv6 && zebra_srv6_is_enable()) {
                vty_out(vty, "  locators\n");
                for (ALL_LIST_ELEMENTS_RO(srv6->locators, node, locator)) {
                        inet_ntop(AF_INET6, &locator->prefix.prefix,