vim-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.
d4cf9fc53e

N/A patches for version.c:

vim-patch:9.0.0192: possible invalid memory access when 'cmdheight' is zero

Problem:    Possible invalid memory access when 'cmdheight' is zero. (Martin
            Tournoij)
Solution:   Avoid going over the end of w_lines[] when w_height is Rows.
            (closes vim/vim#10882)
fdc5d17d58

src/nvim/testdir/test_cmdline.vim

@@ -150,6 +150,11 @@ func Test_changing_cmdheight()
   call term_sendkeys(buf, ":set cmdheight-=2\<CR>")
   call VerifyScreenDump(buf, 'Test_changing_cmdheight_4', {})
 
+  " reducing window size and then setting cmdheight
+  call term_sendkeys(buf, ":resize -1\<CR>")
+  call term_sendkeys(buf, ":set cmdheight=1\<CR>")
+  call VerifyScreenDump(buf, 'Test_changing_cmdheight_5', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XTest_cmdheight')

src/nvim/testdir/test_messages.vim

@@ -376,6 +376,7 @@ func Test_fileinfo_after_echo()
 endfunc
 
 func Test_cmdheight_zero()
+  enew
   set cmdheight=0
   set showcmd
   redraw!
@@ -425,10 +426,13 @@ func Test_cmdheight_zero()
   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

src/nvim/window.c

@@ -6399,6 +6399,13 @@ void command_height(void)
     return;
   }
 
+  // If cmdline_row is smaller than what it is supposed to be for 'cmdheight'
+  // then set old_p_ch to what it would be, so that the windows get resized
+  // properly for the new value.
+  if (cmdline_row < Rows - p_ch) {
+    old_p_ch = Rows - cmdline_row;
+  }
+
   // Find bottom frame with width of screen.
   frp = lastwin_nofloating()->w_frame;
   while (frp->fr_width != Columns && frp->fr_parent != NULL) {