Minor tweaks to error handling.

static/protocol.js

@@ -150,7 +150,7 @@ ServerConnection.prototype.close = function() {
   * @param {message} m - the message to send.
   */
 ServerConnection.prototype.send = function(m) {
-    if(this.socket.readyState !== this.socket.OPEN) {
+    if(!this.socket || this.socket.readyState !== this.socket.OPEN) {
         // send on a closed connection doesn't throw
         throw(new Error('Connection is not open'));
     }

static/sfu.js

@@ -385,7 +385,11 @@ function stopUpMedia(c) {
  */
 function delUpMedia(c) {
     stopUpMedia(c);
-    delMedia(c.id);
+    try {
+        delMedia(c.id);
+    } catch(e) {
+        console.warn(e);
+    }
     c.close(true);
     delete(serverConnection.up[c.id]);
     setButtonsVisibility()
@@ -474,6 +478,8 @@ function setMedia(c, isUp) {
 function delMedia(id) {
     let mediadiv = document.getElementById('peers');
     let peer = document.getElementById('peer-' + id);
+    if(!peer)
+        throw new Error('Removing unknown media');
     let media = document.getElementById('media-' + id);
 
     media.srcObject = null;