check for missing result of rate_ctr_group_alloc()

In case the counter group allocation fails, we must handle this
gracefully and fail the allocation of the parent object, too.

RelateD: OS#2361
Change-Id: I7dad4a4d52fe05f6b990359841b4408df5990e21
diff --git a/src/gprs/gb_proxy.c b/src/gprs/gb_proxy.c
index d95139f..3603e14 100644
--- a/src/gprs/gb_proxy.c
+++ b/src/gprs/gb_proxy.c
@@ -1431,6 +1431,10 @@
 
 	INIT_LLIST_HEAD(&cfg->bts_peers);
 	cfg->ctrg = rate_ctr_group_alloc(tall_bsc_ctx, &global_ctrg_desc, 0);
+	if (!cfg->ctrg) {
+		LOGP(DGPRS, LOGL_ERROR, "Cannot allocate global counter group!\n");
+		return -1;
+	}
 	clock_gettime(CLOCK_REALTIME, &tp);
 
 	return 0;