Detached EventHandlers when running on a Canvas

[rebser]

Issue Description

When running on a Canvas, EventHandlers are leaking.

Steps to Reproduce

Just run for example tinyFaceDetector on a Canvas.

Expected Behavior

face-api should not produce Detached EventHandlers

**Environment

Browser

[rebser]

Turns out the bug is in awaitMediaLoaded.

if (media instanceof env.getEnv().Canvas || isMediaLoaded(media)) resolve(null); doesn't do the trick because it resolves the Promise to null but doesn't return, meaning the EventHandlers for load and error are still being added.

Solution: if (media instanceof env.getEnv().Canvas || isMediaLoaded(media)) { resolve(null); return; }

[vladmandic]

great job tracing it down - do you wan to submit a pr or do you want me to patch it?

[rebser]

Edit: I created a pull request.