Display compiler's error location in stacktrace.

`clojure.lang.Compiler$CompilerException`s carry the reader location of
the error, but not much else. Display the compiler exception's
location description (when present); then show the details from its
original cause.
Updated this for style, but no, that can't ever be `nil` -- it [comes][1] from `Object/getClass` and `Class/getName`, neither of which can return `nil`.

[1]: https://github.com/clojure-emacs/cider-nrepl/blob/6cd778d31fab658ac4a0120269dca940e9a78955/src/cider/nrepl/middleware/stacktrace.clj#L104