patch 8.1.2227: layout wrong if 'lines' changes while cmdline window is open

Problem:    Layout wrong if 'lines' changes while cmdline window is open.
Solution:   Do not restore the window layout if 'lines' changed.
            (closes #5130)
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 57dff41..3f73d3d 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -768,6 +768,36 @@
   bw!
 endfunc
 
+func Test_cmdwin_restore()
+  CheckScreendump
+
+  let lines =<< trim [SCRIPT]
+    call setline(1, range(30))
+    2split
+  [SCRIPT]
+  call writefile(lines, 'XTest_restore')
+
+  let buf = RunVimInTerminal('-S XTest_restore', {'rows': 12})
+  call term_wait(buf, 100)
+  call term_sendkeys(buf, "q:")
+  call VerifyScreenDump(buf, 'Test_cmdwin_restore_1', {})
+
+  " normal restore
+  call term_sendkeys(buf, ":q\<CR>")
+  call VerifyScreenDump(buf, 'Test_cmdwin_restore_2', {})
+
+  " restore after setting 'lines' with one window
+  call term_sendkeys(buf, ":close\<CR>")
+  call term_sendkeys(buf, "q:")
+  call term_sendkeys(buf, ":set lines=18\<CR>")
+  call term_sendkeys(buf, ":q\<CR>")
+  call VerifyScreenDump(buf, 'Test_cmdwin_restore_3', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XTest_restore')
+endfunc
+
 func Test_buffers_lastused()
   " check that buffers are sorted by time when wildmode has lastused
   call test_settime(1550020000)	  " middle