bug#28161: 26.0.50; Narrowing does not work reliably with flyspell

[Liu Hui]

Hi,

When I'm working with a narrowing buffer, `C-g' sometimes cancels the 
narrowing accidentally. I find it only occurs when flyspell-mode is enabled.

Steps to reproduce:

1. Emacs -Q
2. Create a buffer with several text lines, and turn on flyspell-mode
3. Select some text and press `C-x n n' to narrow the buffer
4. Type any letter and press `C-g' (sometimes twice) and `C-f' 
(sometimes optional) quickly

=> "Narrow" in mode-line disappears and all text are visible now

Thanks