patch 9.0.0187: command line height changes when maximizing window height

Problem:    Command line height changes when maximizing window height.
Solution:   Do not change the command line height. (closes #10885)
diff --git a/src/testdir/test_window_cmd.vim b/src/testdir/test_window_cmd.vim
index cfa5b63..e761c21 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -38,6 +38,26 @@
   set ls&vim
 endfunc
 
+func Test_cmdheight_not_changed()
+  set cmdheight=2
+  set winminheight=0
+  augroup Maximize
+    autocmd WinEnter * wincmd _
+  augroup END
+  split
+  tabnew
+  tabfirst
+  call assert_equal(2, &cmdheight)
+
+  tabonly!
+  only
+  set winminwidth& cmdheight&
+  augroup Maximize
+    au!
+  augroup END
+  augroup! Maximize
+endfunc
+
 " Test for jumping to windows
 func Test_window_jump()
   new