PageTemplates: "length" of repeat variables broken

[d-maurer]

BUG/PROBLEM REPORT

Reproduction:

>>> from zope.component import provideAdapter
>>> from zope.traversing.adapters import DefaultTraversable
>>> from Products.PageTemplates.PageTemplate import PageTemplate
>>> from Products.PageTemplates.tests.util import useChameleonEngine
>>> useChameleonEngine(); provideAdapter(DefaultTraversable, (None,))
>>> t = PageTemplate()
>>> t.write('<tal:repeat repeat="x options/seq" content="repeat/x/length" />')
>>> t(seq="abc")
Traceback (most recent call last):
 ...
  File "...Products/PageTemplates/Expressions.py", line 126, in render
    ob = ob()
  File "...zope.tales/src/zope/tales/tales.py", line 526, in length
    return len(self._seq)
TypeError: object of type 'list_iterator' has no len()
...
 - Expression: "repeat/x/length"
 - Filename:   <string>
 - Location:   (line 1: col 44)
 - Arguments:  template: <Products.PageTemplates.PageTemplate.PageTemplate object at 0x7fa804c59d30>
               options: {'seq': 'abc', 'args': ()}
...

Zope 4.x/5.x