BUG/MEDIUM: h2: properly send an RST_STREAM on mux stream error

Some stream errors are detected on the MUX path (eg: H1 response
encoding). The ones forgot to emit an RST_STREAM frame, causing the
client to wait and/or to see the connection being immediately closed.
This is now fixed.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 2af5ffd..28b1684 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -2986,15 +2986,19 @@
 		}
 	}
 
+	/* RST are sent similarly to frame acks */
+	if (h2s->st == H2_SS_ERROR) {
+		cs->flags |= CS_FL_ERROR;
+		if (h2c_send_rst_stream(h2s->h2c, h2s) > 0)
+			h2s->st = H2_SS_CLOSED;
+	}
+
 	if (h2s->flags & H2_SF_BLK_SFCTL) {
 		/* stream flow control, quit the list */
 		LIST_DEL(&h2s->list);
 		LIST_INIT(&h2s->list);
 	}
 
-	if (h2s->st == H2_SS_ERROR)
-		cs->flags |= CS_FL_ERROR;
-
 	return total;
 }