mjit_worker.c: disable running copy job

after MJIT worker stop.

r65928 didn't fix the SEGV. This commit hopes to fix
http://ci.rvm.jp/results/trunk-mjit-wait@silicon-docker/1478576

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65993 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

mjit_worker.c

@@ -1238,6 +1238,10 @@ mjit_worker(void)
         }
     }
 
+    /* Disable dispatching this job in mjit_copy_job_handler while memory allocated by alloca
+       could be expired after finishing this function. */
+    job.finish_p = TRUE;
+
     /* To keep mutex unlocked when it is destroyed by mjit_finish, don't wrap CRITICAL_SECTION here. */
     worker_stopped = TRUE;
 }