MINOR: mux-quic: fix uninitialized return on qc_send

This should fix the github issue #1562.
diff --git a/src/mux_quic.c b/src/mux_quic.c
index c01fcbf..15c8ebc 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -314,7 +314,7 @@
 {
 	struct eb64_node *node;
 	int xprt_wake = 0;
-	int ret;
+	int ret = 0;
 
 	fprintf(stderr, "%s\n", __func__);