[web] fix muledit rendering bug
form.cw_col might be None and explicitly passing None to the selector
chain may crash. Most __call__ methods of selectors are defined as in :
def __call__(self, cls, req, rset, row=None, col=0, **kwargs)
and then manipulate col as if it's an integer.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html