bgpd: tests - add null pointer protection to fix bgp test failures

Signed-off-by: Lou Berger <lberger@labn.net>
diff --git a/tests/bgp_mpath_test.c b/tests/bgp_mpath_test.c
index a953ce9..174d299 100644
--- a/tests/bgp_mpath_test.c
+++ b/tests/bgp_mpath_test.c
@@ -395,7 +395,8 @@
 static int
 global_test_cleanup (void)
 {
-  zclient_free (zclient);
+  if (zclient != NULL)
+    zclient_free (zclient);
   thread_master_free (master);
   return 0;
 }