fix deadlock issue: don't flush_events in main thread when calling st…

…op, override #work_pending? instead

lib/datadog/core/telemetry/worker.rb

@@ -52,8 +52,6 @@ def start
         def stop(force_stop = false, timeout = @shutdown_timeout)
           buffer.close if running?
 
-          flush_events(dequeue) if work_pending?
-
           super
         end
 
@@ -136,6 +134,10 @@ def dequeue
           buffer.pop
         end
 
+        def work_pending?
+          @run_loop || !buffer.empty?
+        end
+
         def buffer_klass
           if Core::Environment::Ext::RUBY_ENGINE == 'ruby'
             Core::Buffer::CRuby