patch 8.0.1160: getting tab-local variable fails after closing window

Problem:    Getting tab-local variable fails after closing window.
Solution:   set tp_firstwin and tp_lastwin. (Jason Franklin, closes #2170)
diff --git a/src/testdir/test_getvar.vim b/src/testdir/test_getvar.vim
index 0f5dff5..d6b6b69 100644
--- a/src/testdir/test_getvar.vim
+++ b/src/testdir/test_getvar.vim
@@ -86,3 +86,19 @@
   call assert_equal(1, gettabwinvar(2, 3, '&nux', 1))
   tabonly
 endfunc
+
+" It was discovered that "gettabvar()" would fail if called from within the
+" tabline when the user closed a window.  This test confirms the fix.
+func Test_gettabvar_in_tabline()
+  let t:var_str = 'value'
+
+  set tabline=%{assert_equal('value',gettabvar(1,'var_str'))}
+  set showtabline=2
+
+  " Simulate the user opening a split (which becomes window #1) and then
+  " closing the split, which triggers the redrawing of the tabline.
+  leftabove split
+  redrawstatus!
+  close
+  redrawstatus!
+endfunc