join the parse_thread only if its joinable (created in this case).

juci/source.cc

@@ -276,6 +276,7 @@ Source::Controller::~Controller() {
   parse_thread_stop=true;
   parsing.lock(); //Be sure not to destroy while still parsing with libclang
   parsing.unlock();
+  if(parse_thread.joinable())
     parse_thread.join();
 }