Fix race condition preventing slide to work on Edge

www/common/sframe-channel.js

@@ -105,6 +105,21 @@ define([
             insideHandlers.push(content);
         }, true);
 
+        // Make sure both iframes are ready
+        var readyHandlers = [];
+        chan.onReady = function (h) {
+            if (typeof(h) !== "function") { return; }
+            readyHandlers.push(h);
+        };
+        chan.ready = function () {
+            chan.whenReg('EV_RPC_READY', function () {
+                chan.event('EV_RPC_READY');
+            });
+            chan.on('EV_RPC_READY', function () {
+                readyHandlers.forEach(function (h) { h(); });
+            });
+        };
+
         var txid;
         window.addEventListener('message', function (msg) {
             var data = JSON.parse(msg.data);

www/common/sframe-common-outer.js

@@ -313,6 +313,8 @@ define([
                 Cryptpad.useTemplate(href, Cryptget, cb);
             });
 
+
+            sframeChan.ready();
             CpNfOuter.start({
                 sframeChan: sframeChan,
                 channel: secret.channel,

www/common/sframe-common.js

@@ -228,6 +228,7 @@ define([
                 Cryptpad.log(data.logText);
             });
 
+            ctx.sframeChan.ready();
             cb(funcs);
         });
     } };