fix(endpoint:controller): wrap saveUpdates in an if(entity) statement

[wkevwang]

Regarding issue #2052

Fixes issue in endpoint controller - when handleEntityNotFound returns null if the entity is not found, it causes saveUpdates to throw an error since updated.save() is called on null. This will result in a 500 response when the entity is not found, instead of the expected 404.

Wrapping saveUpdates in if(entity) will make it return with undefined when the entity is null, which solves the issue.