gbproxy: ensure peer allocation result

gbproxy_peer_alloc() could return NULL which wasn't checked and used
right away. Fix it by making this assumption explicit with
OSMO_ASSERT(); While at it, also format log messages consistently.

Change-Id: Ib10c954e17a479baef31ded54370b35938e00018
diff --git a/src/gprs/gb_proxy.c b/src/gprs/gb_proxy.c
index eb2bbcc..17a0109 100644
--- a/src/gprs/gb_proxy.c
+++ b/src/gprs/gb_proxy.c
@@ -1018,9 +1018,9 @@
 			if (!from_peer) {
 				/* if a PTP-BVC is reset, and we don't know that
 				 * PTP-BVCI yet, we should allocate a new peer */
-				LOGP(DGPRS, LOGL_INFO, "Allocationg new peer for "
-				     "BVCI=%u via NSEI=%u\n", bvci, nsei);
+				LOGP(DGPRS, LOGL_INFO, "Allocationg new peer for BVCI=%u via NSEI=%u\n", bvci, nsei);
 				from_peer = gbproxy_peer_alloc(cfg, bvci);
+				OSMO_ASSERT(from_peer);
 				from_peer->nsei = nsei;
 			}