Allow PTY for paginated shortlog, to prevent stdin read

This workaround only works where PTY jobs are supported.  The real fix
is to give an explicit argument: `:Git shortlog HEAD`.

Resolves: https://github.com/tpope/vim-fugitive/issues/2100

autoload/fugitive.vim

@@ -3802,7 +3802,7 @@ function! fugitive#Command(line1, line2, range, bang, mods, arg, ...) abort
     let stream = exists('*setbufline')
     let do_edit = substitute(s:Mods(a:mods, 'Edge'), '\<tab\>', '-tab', 'g') . 'pedit!'
   elseif pager
-    let allow_pty = 0
+    let allow_pty = get(args, 0, '') is# 'shortlog'
     if pager is# 2 && a:bang && a:line2 >= 0
       let [do_edit, after_edit] = s:ReadPrepare(a:line1, a:line2, a:range, a:mods)
     elseif pager is# 2 && a:bang