Bug 1858657 - Set mShutdown to true to avoid crashing, r=necko-reviewers,valentin

Differential Revision: https://phabricator.services.mozilla.com/D190790

netwerk/cache2/CacheIOThread.cpp

@@ -198,6 +198,9 @@ nsresult CacheIOThread::Init() {
       PR_CreateThread(PR_USER_THREAD, ThreadFunc, this, PR_PRIORITY_NORMAL,
                       PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 128 * 1024);
   if (!mThread) {
+    // Treat this thread as already shutdown.
+    MonitorAutoLock lock(mMonitor);
+    mShutdown = true;
     return NS_ERROR_FAILURE;
   }