patch 8.2.1413: previous tab page not usable from an Ex command

Problem:    Previous tab page not usable from an Ex command.
Solution:   Add the "#" argument for :tabnext et al. (Yegappan Lakshmanan,
            closes #6677)
diff --git a/src/window.c b/src/window.c
index d2e5c5c..75e0495 100644
--- a/src/window.c
+++ b/src/window.c
@@ -3844,6 +3844,7 @@
 win_new_tabpage(int after)
 {
     tabpage_T	*tp = curtab;
+    tabpage_T	*prev_tp = curtab;
     tabpage_T	*newtp;
     int		n;
 
@@ -3893,7 +3894,7 @@
 	newtp->tp_topframe = topframe;
 	last_status(FALSE);
 
-	lastused_tabpage = tp;
+	lastused_tabpage = prev_tp;
 
 #if defined(FEAT_GUI)
 	// When 'guioptions' includes 'L' or 'R' may have to remove or add