Fix issues #1224 & #1213: Don't call this.predict() unless there is a video.

[lindapaiste]

Issue

Reported in #1224 and #1213.

The Facemesh and Handpose models are designed such that they user can instantiated it a with a video and use a facemesh.on("face") callback to process the result of every frame. This chain of continuous prediction begins with a call to this.predict() inside this.loadModel().

This creates an error when no video is provided, as this.predict() is called without any input image. In Facemesh, this logs an error Uncaught (in promise) TypeError: Cannot read property 'height' of undefined. In Handpose the error is avoided by returning [] from this.predict().

Changes

• Added a conditional statement such that this.predict() is only called when there is a video.
• Throw an error in both classes if predict() is called with no image or video.
• JSDoc
  • Fix the incorrect return types on predict().
  • Make all three constructor arguments optional.
  • Add a type for this.model.
• Removed eslint disabling for rules which aren't actually broken.

[joeyklee]

Thanks so much @lindapaiste ! Another really helpful error handling + friendly error message. (sorry it has taken me so long to get to this!)