vim-patch:9.2.0299: runtime(zip): may write using absolute paths (#38810)

Problem:  runtime(zip): may write using absolute paths
          (syndicate)
Solution: Detect this case and abort on Unix, warn in the documentation
          about possible issues

46f530e517

Co-authored-by: Christian Brabandt <cb@256bit.org>
(cherry picked from commit 4aa8969d29)

test/old/testdir/test_plugin_zip.vim

@@ -297,3 +297,22 @@ func Test_zip_fname_evil_path2()
   call assert_match('zipfile://.*::.*tmp/foobar', @%)
   bw!
 endfunc
+
+func Test_zip_fname_evil_path3()
+  CheckNotMSWindows
+  " needed for writing the zip file
+  CheckExecutable zip
+
+  call s:CopyZipFile("evil.zip")
+  defer delete("X.zip")
+  e X.zip
+
+  :1
+  let fname = 'payload.txt'
+  call search('\V' .. fname)
+  exe "normal \<cr>"
+  :w!
+  let mess  = execute(':mess')
+  call assert_match('Path Traversal Attack', mess)
+  bw!
+endfunc