bug#19342: auto-fill scan-error in sh-mode

[Charles A. Roelli]

> From: Glenn Morris <rgm@gnu.org>
> Date: Wed, 10 Dec 2014 16:51:22 -0500
> 
> Package: emacs
> Version: 24.4
> 
> emacs -Q /tmp/foo.sh
> M-x auto-fill-mode
> 
> Type a long string with spaces, past fill-column; eg:
> 
> foo="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaa aaaaaaaaaa
> 
> Auto-fill results in:
> 
> Error: (scan-error "Containing expression ends prematurely" 75 75)

Can't produce this in the latest master, it seems to work fine now.