MINOR: quic: Non checked returned value for cs_new() in h3_decode_qcs()

This should fix CID 1469664 for GH #1546
diff --git a/src/h3.c b/src/h3.c
index a7f0cda..b9e4d5e 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -176,6 +176,9 @@
 		htx->flags |= HTX_FL_EOM;
 
 	cs = cs_new(qcs->qcc->conn, qcs->qcc->conn->target);
+	if (!cs)
+		return 1;
+
 	cs->flags |= CS_FL_NOT_FIRST;
 	cs->ctx = qcs;
 	stream_create_from_cs(cs, &htx_buf);