Only wake up the logwatcher if it is running

This fixes a use-after-destroy of the logwather condition variable
reported in #19

src/fellow_log.c

@@ -5142,7 +5142,8 @@ fellow_logs_rewrite(struct fellow_fd *ffd,
 
 	AZ(pthread_mutex_lock(&ffd->logmtx));
 	ffd->rewriting = 0;
-	AZ(pthread_cond_broadcast(&ffd->watcher_cond));
+	if (ffd->watcher_running)
+		AZ(pthread_cond_broadcast(&ffd->watcher_cond));
 	AZ(pthread_mutex_unlock(&ffd->logmtx));
 	ffd->diag("... done: %fs\n", VTIM_mono() - t0);
 }
@@ -5521,7 +5522,7 @@ fellow_logwatcher_check(struct fellow_fd *ffd)
 
 	DBG("need %s", flw_need_s[need]);
 	AZ(pthread_mutex_lock(&ffd->logmtx));
-	if (ffd->phase == FP_OPEN)
+	if (ffd->phase == FP_OPEN && ffd->watcher_running)
 		AZ(pthread_cond_broadcast(&ffd->watcher_cond));
 	AZ(pthread_mutex_unlock(&ffd->logmtx));
 }
@@ -5554,8 +5555,8 @@ fellow_logwatcher_fini(struct fellow_fd *ffd)
 {
 	CHECK_OBJ_NOTNULL(ffd, FELLOW_FD_MAGIC);
 
-	ffd->watcher_running = 0;
 	AZ(pthread_mutex_lock(&ffd->logmtx));
+	ffd->watcher_running = 0;
 	AZ(pthread_cond_broadcast(&ffd->watcher_cond));
 	AZ(pthread_mutex_unlock(&ffd->logmtx));
 	AZ(pthread_join(ffd->watcher_thread, NULL));