patch 8.0.1222: test functions interfere with each other

Problem:    Test functions interfere with each other.
Solution:   Cleanup tab pages, windows and buffers.  Reset option.
diff --git a/src/testdir/test_tabpage.vim b/src/testdir/test_tabpage.vim
index 239b1b9..95e3c13 100644
--- a/src/testdir/test_tabpage.vim
+++ b/src/testdir/test_tabpage.vim
@@ -475,6 +475,7 @@
 
 func Test_close_on_quitpre()
   " This once caused a crash
+  edit Xtest
   new
   only
   set bufhidden=delete
@@ -489,7 +490,7 @@
   while tabpagenr('$') > 1
     bwipe!
   endwhile
-  1b
+  buf Xtest
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab