fix(vim.net): always pass response body to on_response #38460

Problem:
on_response(err, response) handler doesn't receive a response when an
output buffer or path is supplied to vim.net.request. User might want to
both output output to a file/buffer and also do something with it on
response.

Solution:
If an on_response handler was given, then pass the response to it.

runtime/lua/vim/net.lua

@@ -86,7 +86,7 @@ function M.request(url, opts, on_response)
     elseif res.code ~= 0 then
       err = res.stderr ~= '' and res.stderr or ('Request failed with exit code %d'):format(res.code)
     else
-      if not (opts.outpath or opts.outbuf) then
+      if on_response then
         response = {
           body = res.stdout --[[@as string]],
         }