`bodyPose` and `bodySegmentation` failing to preload in p5 instance mode

[jackbdu]

Creating a new issue to track the progress of this:

@lindapaiste Thank you for adding support for instance mode. I was able to preload most models (ml5.faceMesh, ml5.handPose, ml5.imageClassifier, ml5.neuralNetwork, and ml5.sentiment) but I'm getting an error for ml5.bodyPose. See this minimal sketch demonstrating the issue. I also included my temporary fix in the comments, which creates blank window._incrementPreload() and window._decrementPreload() to avoid this error.

I'm also getting an error for preloading ml5.bodySegmentation in instance mode, and that could be fixed by declaring a global variable let video;.

Originally posted by @jackbdu in https://github.com/ml5js/ml5-next-gen/issues/81#issuecomment-2067780151