Skip creating new buffer if current buffer is empty

This prevents buffer-local commands getting lost that were set before startify
was run. E.g. :Git which is set by fugitive.

plugin/startify.vim

@@ -33,7 +33,7 @@ function! s:update_oldfiles(file)
 endfunction
 
 function! s:genesis()
-  if !argc() && (line2byte('$') == -1)
+  if !argc()
     if get(g:, 'startify_session_autoload') && filereadable('Session.vim')
       source Session.vim
     elseif !get(g:, 'startify_disable_at_vimenter')