BUG/MEDIUM: h2: Close connection if no stream is left an GOAWAY was sent.

When we're closing a stream, is there's no stream left and a goaway was sent,
close the connection, there's no reason to keep it open.

[wt: it's likely that this is needed in 1.8 as well, though it's unclear
 how to trigger this issue, some tests are needed]
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 4fe811a..ae885d9 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -2649,7 +2649,7 @@
 	if (eb_is_empty(&h2c->streams_by_id) &&     /* don't close if streams exist */
 	    ((h2c->conn->flags & CO_FL_ERROR) ||    /* errors close immediately */
 	     (h2c->st0 >= H2_CS_ERROR && !h2c->task) || /* a timeout stroke earlier */
-	     (h2c->flags & H2_CF_GOAWAY_FAILED) ||
+	     (h2c->flags & (H2_CF_GOAWAY_FAILED | H2_CF_GOAWAY_SENT)) ||
 	     (!b_data(&h2c->mbuf) &&  /* mux buffer empty, also process clean events below */
 	      (conn_xprt_read0_pending(h2c->conn) ||
 	       (h2c->last_sid >= 0 && h2c->max_id >= h2c->last_sid))))) {