Fixed issue where anchors not reporting correct position

Fixes issue : https://github.com/kivy/kivy/issues/2254
Nicely spotted sir! Done. Thanks :-)

On 15/06/2014 18:20, matham wrote:
>
> In kivy/core/text/markup.py:
>
> > @@ -209,12 +211,7 @@ def _pre_render(self):
> >              elif item == '[/ref]':
> >                  spop('_ref')
> >              elif not clipped and item[:8] == '[anchor=':
> > -                ref = item[8:-1]
> > -                if len(lines):
> > -                    x, y = lines[-1].x, lines[-1].y
> > -                else:
> > -                    x = y = 0
> > -                self._anchors[ref] = x, y
> > +                options['_anchor'] = item[8:-1]
>
> You should also add a line after line 232 saying |options['_anchor'] = 
> None|, because when shorten is enabled, the anchors should be cleared.
>
> —
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> <https://github.com/kivy/kivy/pull/2259/files#r13786866>.
>