Fail gracefully when view name doesn't match

I'm frequently getting a WSOD during development when I change the machine names of my views that are used in the rule action "Load a list of entities from a VBO View." (Remember, I said "development".) Machine names get cached, and the wrong machine name gets called.

In production, once everything's working, this issue isn't a problem. Therefore, I'm calling it a "feature request."

I have tracked the WSOD to _views_bulk_operations_rules_get_entity_type(). If the view name doesn't match, for whatever reason, I'm pretty much locked out of my site.

Here's a patch that allows that function to fail more gracefully when this happens.