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

This should fix CID 1469657 for GH #1546
diff --git a/src/hq_interop.c b/src/hq_interop.c
index 11d729a..0e2c6cd 100644
--- a/src/hq_interop.c
+++ b/src/hq_interop.c
@@ -73,6 +73,9 @@
 	htx_to_buf(htx, &htx_buf);
 
 	cs = cs_new(qcs->qcc->conn, qcs->qcc->conn->target);
+	if (!cs)
+		return -1;
+
 	cs->ctx = qcs;
 	stream_create_from_cs(cs, &htx_buf);