bug#25181: 25.1.90; move-beginning-of-line doesn't move point

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

Bug does not appear with Emacs -Q, as some fontification in buffer seems 
to trigger it.

Text in buffer:

git reset HEAD test/2.sh

Cursor at pos 16. i.e. beginning of word "test".

C-a doesn't move point.


Watching move-beginning-of-line edebug, at line 6415

     (skip-chars-backward "^\n")

jumps correctly to BOL.

Error results from following later on:

     (setq first-vis-field-value
       (constrain-to-field first-vis orig (/= arg 1) t nil))

Here first-vis-field-value is set to orig, i.e. pos 16, where it jumps 
back-to, not leaving point at BOL.

When C-a is called at or from behind word "test", it stops at pos 16, 
when called before it reaches BOL


In GNU Emacs 25.1.90.1 (i686-pc-linux-gnu, GTK+ Version 3.14.5)
  of 2016-11-29
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description:    Debian GNU/Linux 8.6 (jessie)

Configured using:
  'configure --with-modules'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS NOTIFY ACL GNUTLS
LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
MODULES

Important settings:
   value of $LANG: de_DE.utf8
   value of $XMODIFIERS: @im=ibus
   locale-coding-system: utf-8-unix

Major mode: Shell-script

Minor modes in effect:
   shell-dirtrack-mode: t
   diff-auto-refine-mode: t
   highlight-changes-visible-mode: t
   show-paren-mode: t
   save-place-mode: t
   override-global-mode: t
   sh-electric-here-document-mode: t
   winner-mode: t
   tooltip-mode: t
   mouse-wheel-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent messages:

Result: 16 (#o20, #x10, ?\C-p)
Pos. 263500 als register "a" [2 times]
Back to top level [2 times]
move-beginning-of-line
Mark set
Pos. 263500 als register "a"
Mark set
nil
move-beginning-of-line