patch 8.2.0599: Netbeans interface insufficiently tested

Problem:    Netbeans interface insufficiently tested.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5921)
diff --git a/src/netbeans.c b/src/netbeans.c
index 4ff9085..ad049a2 100644
--- a/src/netbeans.c
+++ b/src/netbeans.c
@@ -743,6 +743,7 @@
 	nbdebug(("EVT: %s", buf));
 	// nb_send(buf, "netbeans_end");    avoid "write failed" messages
 	nb_send(buf, NULL);
+	buf_list[i].bufp = NULL;
     }
 }