patch 9.0.0191: messages test fails; window size incorrect

Problem:    Messages test fails; window size incorrect when 'cmdheight' is
            made smaller.
Solution:   Properly cleanup after test with cmdheight zero.  Resize windows
            correctly when 'cmdheight' gets smaller.
diff --git a/src/testdir/test_messages.vim b/src/testdir/test_messages.vim
index 1f1bb9b..3c3712e 100644
--- a/src/testdir/test_messages.vim
+++ b/src/testdir/test_messages.vim
@@ -388,6 +388,7 @@
 endfunc
 
 func Test_cmdheight_zero()
+  enew
   set cmdheight=0
   set showcmd
   redraw!
@@ -437,10 +438,13 @@
   7
   call feedkeys(":\"\<C-R>=line('w0')\<CR>\<CR>", "xt")
   call assert_equal('"1', @:)
-  bwipe!
 
+  bwipe!
+  bwipe!
   set cmdheight&
   set showcmd&
+  tabnew
+  tabonly
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab