fix: check tech error before pause loaders (#969)

A failed poster image may trigger an error event from the tech. This shouldn't cause us to pause our loaders, though.
Instead, we should verify that there's an actual error object on the tech before proceeding with pausing the loaders.

src/videojs-http-streaming.js

@@ -526,7 +526,9 @@ class VhsHandler extends Component {
     });
 
     this.on(this.tech_, 'error', function() {
-      if (this.masterPlaylistController_) {
+      // verify that the error was real and we are loaded
+      // enough to have mpc loaded.
+      if (this.tech_.error() && this.masterPlaylistController_) {
         this.masterPlaylistController_.pauseLoading();
       }
     });

test/master-playlist-controller.test.js

@@ -3228,9 +3228,13 @@ QUnit.test('pauses subtitle segment loader on tech errors', function(assert) {
 
   masterPlaylistController.subtitleSegmentLoader_.pause = () => pauseCount++;
 
+  this.player.tech_.error = () => 'foo';
   this.player.tech_.trigger('error');
 
   assert.equal(pauseCount, 1, 'paused subtitle segment loader');
+
+  assert.equal(this.env.log.error.calls, 1, '1 media error logged');
+  this.env.log.error.reset();
 });
 
 QUnit.test('disposes subtitle loaders on dispose', function(assert) {

test/videojs-http-streaming.test.js

@@ -304,6 +304,36 @@ QUnit.test('the VhsHandler instance is referenced by player.vhs', function(asser
   assert.equal(this.env.log.warn.calls, 1, 'warning logged');
 });
 
+QUnit.test('tech error may pause loading', function(assert) {
+  this.player.src({
+    src: 'manifest/playlist.m3u8',
+    type: 'application/vnd.apple.mpegurl'
+  });
+  this.clock.tick(1);
+
+  const vhs = this.player.tech_.vhs;
+  const mpc = vhs.masterPlaylistController_;
+  let pauseCalled = false;
+
+  mpc.pauseLoading = () => {
+    pauseCalled = true;
+  };
+
+  this.player.tech_.error = () => null;
+  this.player.tech_.trigger('error');
+
+  assert.notOk(pauseCalled, 'no video el error attribute, no pause loading');
+
+  this.player.tech_.error = () => 'foo';
+  this.player.tech_.trigger('error');
+
+  assert.ok(pauseCalled, 'video el error and trigger pauses loading');
+
+  assert.equal(this.env.log.error.calls, 1, '1 media error logged');
+  this.env.log.error.reset();
+
+});
+
 QUnit.test('a deprecation notice is shown when using player.dash', function(assert) {
   this.player.src({
     src: 'manifest/playlist.m3u8',