vim-patch:9.1.1139: [fifo] is not displayed when editing a fifo

Problem:  [fifo] is not displayed when editing a fifo
          (after v7.4.2189)
Solution: stat the filename and detect the type correctly

fixes: vim/vim#16702
closes: vim/vim#16705

f1c3134ee1

Co-authored-by: Christian Brabandt <cb@256bit.org>

src/nvim/buffer.c

@@ -305,6 +305,8 @@ int open_buffer(bool read_stdin, exarg_T *eap, int flags_arg)
     if (read_fifo) {
       curbuf->b_p_bin = save_bin;
       if (retval == OK) {
+        // don't add READ_FIFO here, otherwise we won't be able to
+        // detect the encoding
         retval = read_buffer(false, eap, flags);
       }
     }