[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.

from cubicweb.devtools.testlib import CubicWebTC
from cubicweb.web import uicfg

class UICFGTC(CubicWebTC):

    def test(self):
        self.skip('write some tests')

if __name__ == '__main__':
    from logilab.common.testlib import unittest_main
    unittest_main()