fix: update HasFunction method to discern between regular knots and function knots.

[Necronomison]

Context:

For detailed information on the problem, please see the issue posted here:
#928

In short, the issue seems to be that Story.cs's method HasFunction doesn't discern between regular knots and function knots. It calls upon KnotContainerWithName to check if the container is there, but this doesn't distinguish function knots.

Solution:

Debugging and looking at the structure of a regular knot vs function knot Container object, the only difference I can note is that function knots contain a PopFunction command at the end of their contents. I've leveraged this for a (hacky) fix to check if the knot container retrieved is indeed a function.

If you know of a better way to do this, please make a suggestion!