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/dumps/Test_cmdwin_restore_1.dump b/src/testdir/dumps/Test_cmdwin_restore_1.dump
new file mode 100644
index 0000000..8ac0295
--- /dev/null
+++ b/src/testdir/dumps/Test_cmdwin_restore_1.dump
@@ -0,0 +1,12 @@
+|0+0&#ffffff0| @73
+|[+1&&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|T|o|p
+|0+0&&| @73
+|[+1&&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|T|o|p
+|:+0#4040ff13&> +0#0000000&@73
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|[+3#0000000&|C|o|m@1|a|n|d| |L|i|n|e|]| @42|1|,|0|-|1| @9|A|l@1
+|:+0&&| @73
diff --git a/src/testdir/dumps/Test_cmdwin_restore_2.dump b/src/testdir/dumps/Test_cmdwin_restore_2.dump
new file mode 100644
index 0000000..ce0b2b5
--- /dev/null
+++ b/src/testdir/dumps/Test_cmdwin_restore_2.dump
@@ -0,0 +1,12 @@
+>0+0&#ffffff0| @73
+|1| @73
+|[+3&&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|T|o|p
+|0+0&&| @73
+|1| @73
+|2| @73
+|3| @73
+|4| @73
+|5| @73
+|6| @73
+|[+1&&|N|o| |N|a|m|e|]| |[|+|]| @43|1|,|1| @11|T|o|p
+| +0&&@74
diff --git a/src/testdir/dumps/Test_cmdwin_restore_3.dump b/src/testdir/dumps/Test_cmdwin_restore_3.dump
new file mode 100644
index 0000000..1cc0f3f
--- /dev/null
+++ b/src/testdir/dumps/Test_cmdwin_restore_3.dump
@@ -0,0 +1,18 @@
+>0+0&#ffffff0| @73
+|1| @73
+|2| @73
+|3| @73
+|4| @73
+|5| @73
+|6| @73
+|7| @73
+|8| @73
+|9| @73
+|1|0| @72
+|1@1| @72
+|1|2| @72
+|1|3| @72
+|1|4| @72
+|1|5| @72
+|1|6| @72
+@57|1|,|1| @10|T|o|p| 
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