Ensure we have a valid currentBlog before checking for local changes. Fixes #793.
Check for valid blog and context before running refreshBlogContentTask
Yet another valid current blog check. This fixes #804
Cancel the RefreshBlogContentTask if an invalid blog or context is passed to the constructor.
Merge pull request #811 from wordpress-mobile/issue/793-npe-local-changes

Ensure we have a valid currentBlog before checking for local changes.