Several problems in update 8103

I have uncovered two problems (semi-related) in Search API's update #8103.

1) If you have an index which uses the node_status processor with no additional configuration (i.e., it's an empty array), it will not be updated correctly because the update hook is checking if $processor['node_status'] is not empty, as opposed to non-null.

2) If you have a view which uses a Search API index that uses the node_status processor, entity type definition updates performed during the same update batch (even by other modules) may go kaboom. This is because Views will try to rebuild its own set of caches, and in so doing, will invoke a Search API hook. Which, in turn, will ultimately try to load all processor plugin definitions, including node_status (I'm glossing over the specifics because the call chain is very long, and I can post steps to reproduce if requested) -- which will result in a SearchApiException because update 8103 didn't bother to clear the cached processor plugin definitions.

I'll attach a patch which fixes both issues.