fix in queue clear

include/c11log/details/blocking_queue.h

@@ -97,7 +97,7 @@ public:
     {
     	{
 			std::unique_lock<std::mutex> ul(mutex_);
-			q_.swap(queue_t());
+			queue_t().swap(q_);
 		}
 		item_popped_cond_.notify_all();	    
     }

src/test.cpp

@@ -70,7 +70,8 @@ void popper(Q* q)
 	string output;
 	while(active)
 	{		
-		q->pop(output);			
+		//q->pop(output);			
+		q->clear();
 		++pop_count;
 	}
 }