Fix a bug in the driver, closing channel too soon

luprex/cpp/drv/driver-common.cpp

@@ -449,11 +449,13 @@ class Driver {
             }
             if (chan.nbytes == 0) {
                 if (engw.get_channel_released(&engw, chan.chid)) {
+                    if (BIO_pending(chan.send_bio) == 0) {
                         close_channel(chan, "");
                         any_released = true;
                     }
                 }
             }
+        }
 
         // Delete any released channels
         if (any_released) {