[WebGL] AVPPlayerClose produces error MediaError.MEDIA_ERR_SRC_NOT_SUPPORTED

[jarruda]

Describe the bug
When the AVPPlayerClose method is invoked in the jslib plugin for WebGL, it sets the src attribute of the Video element to an empty string and invokes the load method on it to release the resources for the element.

This action results in the onerror handler being invoked with the error MediaError.MEDIA_ERR_SRC_NOT_SUPPORTED, which invokes console.log with the error. This behavior has been observed in Chrome, at least.

The HTML standard recommends removing the src attribute and invoking load instead of setting it to an empty string. We've applied this change to our codebase and it appears to work well.

Your Setup (please complete the following information):

• Unity version: 2018.4.25f1
• AVPro Video version: [AVProVideo] Initialising AVPro Video (script v1.11.4 plugin v1.9.17) on ANGLE (Intel(R) UHD Graphics 620 Direct3D11 vs_5_0 ps_5_0)/OpenGL ES 3.0 (WebGL 2.0) (MT False) on WebGLPlayer Windows 10
• Operating system version: ^
• Device model: ^
• Video specs (resolution, frame-rate, codec, file size): n/a

To Reproduce

1. Load WebGL player into Chrome browser.
2. Load a video into a MediaPlayer.
3. Destroy the MediaPlayer
4. Observe log.

Logs

Error: video not supported (errorcode=4) color:red;

Patch:

        // Setting 'src' to an empty string results in the onerror handler being invoked and producing log noise on Chrome.
        // Removing the src attribute and invoking load is a recommended best practice in the HTML Standard.
        // See https://html.spec.whatwg.org/multipage/media.html#best-practices-for-authors-using-media-elements
        vid.pause();
        vid.removeAttribute("src"); // Previous: vid.src = "";
        vid.load();

[AndrewRH]

Thanks @jarruda for this great suggestion - we will roll this into the next release.