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: #16702
closes: #16705

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/buffer.c

@@ -275,6 +275,8 @@ open_buffer(
 	{
 	    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);
 	}
 #endif