fix(queues): shutdown flag needs to be checked while waiting (#11456)

The previous fix (#11376) to enable batching during shutdown failed to check
the shutdown flag while waiting for more items to batch.  If the coalescing
delay was large enough, this could cause the last batch to be lost.

kong/tools/queue.lua

@@ -234,17 +234,19 @@ function Queue:process_once()
 
   -- We've got our first entry from the queue.  Collect more entries until max_coalescing_delay expires or we've collected
   -- max_batch_size entries to send
-  if ngx.worker.exiting() then
-    -- minimize coalescing delay during shutdown to quickly process remaining entries
-    self.max_coalescing_delay = COALESCE_MIN_TIME
-  end
   while entry_count < self.max_batch_size
     and self.max_coalescing_delay - (now() - data_started) >= COALESCE_MIN_TIME
   do
     -- Instead of waiting for the coalesce time to expire, we cap the semaphore wait to COALESCE_POLL_TIME
     -- so that we can check for worker shutdown periodically.
     local wait_time = math_min(self.max_coalescing_delay - (now() - data_started), COALESCE_POLL_TIME)
 
+    if ngx.worker.exiting() then
+      -- minimize coalescing delay during shutdown to quickly process remaining entries
+      self.max_coalescing_delay = COALESCE_MIN_TIME
+      wait_time = COALESCE_MIN_TIME
+    end
+
     ok, err = self.semaphore:wait(wait_time)
     if not ok and err ~= "timeout" then
       self:log_err("could not wait for semaphore: %s", err)