Save a call to stopThreadedIOIfNeeded() for the base case.

Probably no performance changes, but the code should be trivial to
read as in "No threading? Use the normal function and return".

src/networking.c

@@ -2997,9 +2997,9 @@ int handleClientsWithPendingWritesUsingThreads(void) {
     int processed = listLength(server.clients_pending_write);
     if (processed == 0) return 0; /* Return ASAP if there are no clients. */
 
-    /* If we have just a few clients to serve, don't use I/O threads, but the
-     * boring synchronous code. */
-    if (stopThreadedIOIfNeeded()) {
+    /* If I/O threads are disabled or we have few clients to serve, don't
+     * use I/O threads, but thejboring synchronous code. */
+    if (server.io_threads_num == 1 || stopThreadedIOIfNeeded()) {
         return handleClientsWithPendingWrites();
     }