In order to add a new key to both __objects and __functions dicts on jsinterp.py, it is
necessary to first verify if a key was present and if not, create the key and
assign it to a value.
However, this can be done with a single step using dict setdefault method.
We need a proper lexer to be able to understand YouTube's code, which contains /* inside of strings.
For now it's sufficient to just disable comment support altogether.
Fixes#4976, fixes#4979, fixes#4980, fixes#4981, fixes#4982.
Closes#4977.