GPRS: Fix crash when the peer can not be found...

Use UINT_MAX (or -1) if the peer can not be found.
diff --git a/openbsc/src/gprs/gb_proxy.c b/openbsc/src/gprs/gb_proxy.c
index b6fbac7..936b102 100644
--- a/openbsc/src/gprs/gb_proxy.c
+++ b/openbsc/src/gprs/gb_proxy.c
@@ -320,11 +320,11 @@
 	} else if (TLVP_PRESENT(tp, BSSGP_IE_ROUTEING_AREA)) {
 		peer = peer_by_rac(TLVP_VAL(tp, BSSGP_IE_ROUTEING_AREA));
 		LOGPC(DGPRS, LOGL_INFO, "routing by RAC to peer BVCI=%u\n",
-			peer->bvci);
+			peer ? peer->bvci : -1);
 	} else if (TLVP_PRESENT(tp, BSSGP_IE_LOCATION_AREA)) {
 		peer = peer_by_lac(TLVP_VAL(tp, BSSGP_IE_LOCATION_AREA));
 		LOGPC(DGPRS, LOGL_INFO, "routing by LAC to peer BVCI=%u\n",
-			peer->bvci);
+			peer ? peer->bvci : -1);
 	} else
 		LOGPC(DGPRS, LOGL_INFO, "\n");