Merge remote-tracking branch 'origin/master' into tyriar/merge_master_to_v3

This pulls in PR #933 which was merged in error to master not v3 and also 2.9.2
release stuff.

src/addons/attach/attach.ts

@@ -59,6 +59,9 @@ export function attach(term, socket, bidirectional, buffered) {
   };
 
   term._sendData = function(data) {
+    if (socket.readyState !== 1) {
+      return;
+    }
     socket.send(data);
   };