fix(powershell): wrong length allocation for ":%w !" #20530

Problem:
The calculation of `len` in `make_filter_cmd` for powershell falls short
by one character for the following ex command:
  :%w !sort
This command satisfies these conditions:
  - `itmp` is not null
  - `otmp` is null
__NOTE__ that other shells circumvent this bug only because of `len`
allocation for six extra characters: a pair of curly braces and four
spaces:
  https://github.com/neovim/neovim/blob/cfdb4cbada8c65aa57e69776bcc0f7b8b298317a/src/nvim/ex_cmds.c#L1551-L1554
If allocation for these six characters are removed, then bash also faces
the same bug.

Solution:
Add allocation for 6 extra bytes. 1 would do, but let's keep powershell
in sync with other shells as much as possible.

1 files changed, 29 insertions, 0 deletions

diff --git a/test/functional/vimscript/system_spec.lua b/test/functional/vimscript/system_spec.lua
index f099b4a36e..7ada1c4bea 100644
--- a/test/functional/vimscript/system_spec.lua
+++ b/test/functional/vimscript/system_spec.lua
@@ -662,4 +662,33 @@ describe('shell :!', function()
         1]])
     end
   end)
+
+  it(':{range}! without redirecting to buffer', function()
+    local screen = Screen.new(500, 10)
+    screen:attach()
+    insert([[
+      3
+      1
+      4
+      2]])
+    feed(':4verbose %w !sort<cr>')
+    if is_os('win') then
+      screen:expect{
+        any=[[Executing command: .?sort %< .*]]
+      }
+    else
+      screen:expect{
+        any=[[Executing command: .?%(sort%) %< .*]]
+
+      }
+    end
+    feed('<CR>')
+    helpers.set_shell_powershell(true)
+    feed(':4verbose %w !sort<cr>')
+    screen:expect{
+      any=[[Executing command: .?& { Get%-Content .* | & sort }]]
+    }
+    feed('<CR>')
+    helpers.expect_exit(command, 'qall!')
+  end)
 end)