patch 9.0.0665: setting 'cmdheight' has no effect if last window was resized

Problem:    Setting 'cmdheight' has no effect if last window was resized.
Solution:   Do apply 'cmdheight' when told to.  Use the frame height instead
            of the cmdline_row.  (closes #11286)
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 00939f9..3cfdd76 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -248,6 +248,13 @@
 
   let lines =<< trim END
       set cmdheight=1 laststatus=2
+      func EchoTwo()
+        set laststatus=2
+        set cmdheight=5
+        echo 'foo'
+        echo 'bar'
+        set cmdheight=1
+      endfunc
   END
   call writefile(lines, 'XTest_cmdheight', 'D')
 
@@ -272,6 +279,10 @@
   call term_sendkeys(buf, ":set cmdheight=1\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_5', {})
 
+  " setting 'cmdheight' works after outputting two messages
+  call term_sendkeys(buf, ":call EchoTwo()\<CR>")
+  call VerifyScreenDump(buf, 'Test_changing_cmdheight_6', {})
+
   " clean up
   call StopVimInTerminal(buf)
 endfunc