Ensure entity id exists in results before render in entity_plugin_row_entity_view::render()

While testing #1266036: Add generic Views entity tables with fields and relationships and #1231512: Use real Relationships instead of level magic in Views integration I came across these notice / exception:

Notice: Undefined offset: 163 in entity_plugin_row_entity_view->render() (Line 106 of modules/entity/views/plugins/entity_plugin_row_entity_view.inc).

EntityMalformedException: Missing bundle property on entity of type node. in entity_extract_ids() (Line 7414 of drupal/includes/common.inc).

The root cause of this was that the search index contained a nid of an already deleted node. Tomas ensured me that this never (should) happens - but I think for the sake of defensive coding we should add the attached patch. :)