Handle missing properties in controllers.

Don't blow up when someone tries to access a property (like a taglib namespace)
added via the missing property mechanism on the controller metaclass.

This was reported as https://github.com/tomdcc/grails-miniprofiler/issues/8 but is actually a bug in the profiler plugin code. I can only presume that properties added to controllers in earlier versions of grails were added directly rather than via missing property, so the issue wouldn't have been a problem then.