gb_proxy_peer: fix NULL pointer dereference in gbproxy_sgsn_alloc()

LOGPSGSN_CAT() dereferences sgsn->nse in order to get NSEI.

Change-Id: I1c592dd6f0da5f167290f38de3b30a1a04c4313d
Fixes: CID#215868
diff --git a/src/gbproxy/gb_proxy_peer.c b/src/gbproxy/gb_proxy_peer.c
index 863bcce..544eb5f 100644
--- a/src/gbproxy/gb_proxy_peer.c
+++ b/src/gbproxy/gb_proxy_peer.c
@@ -364,7 +364,8 @@
 
 	sgsn->nse = gbproxy_nse_alloc(cfg, nsei, true);
 	if (!sgsn->nse) {
-		LOGPSGSN_CAT(sgsn, DOBJ, LOGL_INFO, "Could not allocate NSE(%05u) for SGSN\n", nsei);
+		LOGP(DOBJ, LOGL_ERROR, "Could not allocate NSE(%05u) for SGSN(%s)\n",
+		     nsei, sgsn->name);
 		goto free_sgsn;
 	}