GUACAMOLE-346: Playback must take into account that seeking is asynchronous.

guacamole-common-js/src/main/webapp/modules/SessionRecording.js

@@ -415,7 +415,7 @@ Guacamole.SessionRecording = function SessionRecording(tunnel) {
     var continuePlayback = function continuePlayback() {
 
         // Advance to next frame
-        seekToFrame(currentFrame + 1);
+        seekToFrame(currentFrame + 1, function playbackSeekComplete() {
 
             // If frames remain after advancing, schedule next frame
             if (currentFrame + 1 < frames.length) {
@@ -442,6 +442,8 @@ Guacamole.SessionRecording = function SessionRecording(tunnel) {
             else
                 recording.pause();
 
+        });
+
     };
 
     /**