don't track progress until ready

Delay manual progress checks until the tech is ready to avoid errors. The Flash tech errors if buffered() is called before the SWF has loaded, for instance.

src/js/tech/tech.js

@@ -98,7 +98,9 @@ class Tech extends Component {
     this.manualProgress = true;
 
     // Trigger progress watching when a source begins loading
-    this.trackProgress();
+    this.one('ready', () => {
+      this.trackProgress();
+    });
   }
 
   manualProgressOff() {
@@ -109,6 +111,7 @@ class Tech extends Component {
   }
 
   trackProgress() {
+    this.stopTrackingProgress();
     this.progressInterval = this.setInterval(Fn.bind(this, function(){
       // Don't trigger unless buffered amount is greater than last time
 

test/unit/tech/tech.test.js

@@ -61,14 +61,26 @@ test('stops manual timeupdates while paused', function() {
 });
 
 test('should synthesize progress events by default', function() {
-  var progresses = 0, tech;
+  var progresses = 0, bufferedPercent = 0.5, tech;
   tech = new Tech();
   tech.on('progress', function() {
     progresses++;
   });
+  tech.bufferedPercent = function() {
+    return bufferedPercent;
+  };
+
+  this.clock.tick(500);
+  equal(progresses, 0, 'waits until ready');
 
+  tech.trigger('ready');
   this.clock.tick(500);
   equal(progresses, 1, 'triggered one event');
+
+  tech.trigger('ready');
+  bufferedPercent = 0.75;
+  this.clock.tick(500);
+  equal(progresses, 2, 'repeated readies are ok');
 });
 
 test('dispose() should stop time tracking', function() {