journal: reset the offline state if blocking signals fails

journal_file_set_offline() sets OFFLINE_SYNCING before it starts the
offline thread. If the first pthread_sigmask() fails, it returns without
starting the thread and leaves the state at OFFLINE_SYNCING. The next
journal_file_set_offline_thread_join() then calls pthread_join() on a
thread that was never created.

Set OFFLINE_JOINED, as the error path of pthread_create() does.

(cherry picked from commit db2b225a30da26d0939f1f6d6c4b524bd2240900)

src/shared/journal-file-util.c

@@ -377,8 +377,10 @@ int journal_file_set_offline(JournalFile *f, bool wait) {
                 assert_se(sigdelset(&ss, SIGBUS) >= 0);
 
                 r = pthread_sigmask(SIG_BLOCK, &ss, &saved_ss);
-                if (r > 0)
+                if (r > 0) {
+                        f->offline_state = OFFLINE_JOINED;
                         return -r;
+                }
 
                 r = pthread_create(&f->offline_thread, NULL, journal_file_set_offline_thread, f);