[sobjects/notification] fix broken email notifications In https://hg.logilab.org/review/cubicweb/rev/8caa109dfe945592a34904bb56971cc57d1c6084 EntityView.w become a method using EntityView._w In notifications we reset "self.w" for every notifications since we handle multiple streams. We should set "self._w" to None instead, otherwise subsequent calls to "self.w()" will fail with TypeError: 'NoneType' object is not callable.

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))