Handle expired timers in basic_stream transfer_op

Previously, the code only handled expired timers when the buffer was empty.

test/beast/core/basic_stream.cpp

@@ -656,6 +656,17 @@ public:
             ioc.restart();
         }
 
+        {
+            // non-empty buffer, timeout
+            test_server srv("*", ep, log);
+            stream_type s(ioc);
+            s.socket().connect(srv.local_endpoint());
+            s.expires_after(std::chrono::seconds(0));
+            s.async_write_some(cb, handler(error::timeout, 0));
+            ioc.run();
+            ioc.restart();
+        }
+
         // abandoned operation
         {
             stream_type s(ioc);