Fixes an issue where merging an emtpy result set could cause a crash.

Renames a method for consistency.
Reorganizes some code to remove an unnecessary method.
Sets the has more posts flag to false if no resuls are returned.
Fetch existing object and bail if there is an error or the object doesn't exist.
Merge pull request #1796 from wordpress-mobile/issues/1795-merge-crash

Fixes an issue where merging an emtpy result set could cause a crash.