do not try to acquire RW lock for termination

fixes #3783

Author: vladak

opengrok-web/src/main/java/org/opengrok/web/api/v1/suggester/provider/service/impl/SuggesterServiceImpl.java

@@ -412,6 +412,10 @@ public void waitForInit(long timeout, TimeUnit unit) throws InterruptedException
     /** {@inheritDoc} */
     @Override
     public void close() {
+        if (suggester != null) {
+            suggester.terminate();
+        }
+
         lock.writeLock().lock();
         try {
             scheduler.shutdownNow();

suggester/src/main/java/org/opengrok/suggest/Suggester.java

@@ -603,13 +603,19 @@ public List<Entry<BytesRef, Integer>> getSearchCounts(
         return data.getSearchCountsSorted(field, page, pageSize);
     }
 
+    /**
+     * Do not allow more suggester rebuilds.
+     */
+    public void terminate() {
+        terminating = true;
+    }
+
     /**
      * Closes opened resources.
      */
     @Override
     public void close() {
         executorService.shutdownNow();
-        terminating = true;
         projectData.values().forEach(f -> {
             try {
                 f.close();