Fixed repeat syntax in multi input to also work in Zope 4.5.

[mauritsvanrees]

I now use path expression index repeat/widget/index. When repeat/widget/index is callable, this will call it, otherwise you simply get the value. This should work in older and newer Zope.

Fixes #116

Strangely, in my case after this I get a different error:

   - __traceback_info__: (view.key_widgets[index])
  Module <string>, line 1, in <module>
IndexError: list index out of range

When I check, view.key_widgets (in z3c.form) is an empty list. So there is more going on here, but this seems specific to my form.
But the fix should be good.

Note that this template is an override for a template in z3c.form, where it has the same problem, just like a few other templates.

[mauritsvanrees]

@jenkins-plone-org please run jobs

[jensens]

nice catch :/

[petri]

@mauritsvanrees I appear to have the exact same issue as you. On Plone 5.2.2, Python 3.7.3 on MacOS. My form is using the datagridfield. Strangely enough, it was working first, I have no idea what triggered the issue in #116. After upgrade to 3.2.2 I see the IndexError: list index out of range as well.