correct StackOverflowEerror from rendering `java.nio.Path`

[Groostav]

the java.nio.Path interface is recursively iterable on Path. This causes a stack-overflow in ST4's representation as it is never able to find an element that isnt iterable, so it calls convertAnythingIteratableToIterator all-the-way-down.

java.nio.Path implements Iterable<java.nio.Path>,

eg:

var path = Paths.get("some/path");
Path first = path.iterator().next(); //== "some"
Path firstFirst = first.iterator().next(); //== "some"
Path firstFirstFirst = firstFirst.iterator().next(); //== "some"

and so on.

This really does not play nicely with convertAnythingIteratableToIterator: This behavior means, even if you supply a converter for java.nio.path, ST4 never identifies it as a POJO and so never asks for a renderer.

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suggestions:

• could rewrite the convertAnything to keep a stack of elements that it checks against, if it finds that asking for iterable conversions ever produces the same value => we're probably in an infinite loop => take some action
• could try to restructure to ask if a representation exists for the object before trying to iterate over it.
• a simple-ish fix would be to look for instances of Collection rather than Iterable; given that Iterable is used in some infinite sequences, this would likely help there too.

I'm swamped, but I need this so I could create a PR if needed. In the mean time I'm going to twiddle my thumbs for a while.

[Groostav]

the more I think about it, what is the rationale for converting to iterable before checking if the user provided an explicit converter?