Ancient user watch filters may be configured with strings that
are not valid label names, e.g. "plugins/defaultuser". At the time
these were created the user was expecting to match a project. Now
they blow up the strict checking in LabelType trying to setup an
object for EqualsLabelPredicate to fail to match.
Be more lenient here to allow the label to fail to match.
Change-Id: I52d45456c67924e1981fbbe52a62adfceeebe869
8d516ca9dd