fix(ui): "resize -1" with cmdheight=0 #24758

Problem:
Crash from:

    set cmdheight=0 redrawdebug=invalid
    resize -1

Solution:
Do not invalidate first `p_ch` `msg_grid` rows in `update_screen` when
scrolling the screen down after displaying a message, because they may
be used later for drawing cmdline.
Fixes #22154

1 files changed, 20 insertions, 0 deletions

diff --git a/test/functional/ui/cmdline_spec.lua b/test/functional/ui/cmdline_spec.lua
index 6baad28dad..497b2e7f4c 100644
--- a/test/functional/ui/cmdline_spec.lua
+++ b/test/functional/ui/cmdline_spec.lua
@@ -1021,6 +1021,26 @@ describe('cmdheight=0', function()
     screen:attach()
   end)
 
+  it("with redrawdebug=invalid resize -1", function()
+    command("set redrawdebug=invalid cmdheight=0 noruler laststatus=0")
+    screen:expect{grid=[[
+      ^                         |
+      {1:~                        }|
+      {1:~                        }|
+      {1:~                        }|
+      {1:~                        }|
+    ]]}
+    feed(":resize -1<CR>")
+    screen:expect{grid=[[
+      ^                         |
+      {1:~                        }|
+      {1:~                        }|
+      {1:~                        }|
+                               |
+    ]]}
+    assert_alive()
+  end)
+
   it("with cmdheight=1 noruler laststatus=2", function()
     command("set cmdheight=1 noruler laststatus=2")
     screen:expect{grid=[[