process hanging in embeded mode on exception

As a FUP of #221 which provided a new pathway to see the exception,
but does not prevent the "hanging" in an other pathway.

The simplest scenario is that we have a hanging python process by using this clojure code crash.clj

(ns train
  (:require [libpython-clj2.python :refer [py.- py.] :as py]
            [libpython-clj2.python.ffi :as ffi]))

(def locked (ffi/lock-gil))
(py/import-module "not existing")

and load it in embedded mode using manual-gil via:

export JDK_JAVA_OPTIONS="-Dlibpython_clj.manual_gil=true"
python -c 'from clojurebridge import cljbridge;cljbridge.load_clojure_file(clj_file="crash.clj")'

The exception thrown by python on the last line in crash.clj is swallowed by either clojurebridge or libpython-clj and the process hangs forever.

Start by reproducing the hang with crash.clj, ffi/lock-gil, py/import-module, and clojurebridge.load_clojure_file under manual-gil. Trace how the exception from the missing module is handled between clojurebridge and libpython-clj; done means the embedded process terminates or returns instead of hanging and the exception remains visible.