Check for a nil topic before loading more.

Avoids a rare crash at launch in certain situations.
Minor code style fix and removes a commented method.
Skip fetching a new image from the cache and just copy instead.

This is a work around for an issue retriving some images from the cache.
Bumping version to 4.2.
Added sanity check when note's blog is 0

see #1915
Compute button spacing delta via intrinsicContentSize

Avoids potentially triggering recursion by inspecting a subview.
Merge pull request #1931 from wordpress-mobile/issues/1926-autolayout-crash

Compute button spacing delta via intrinsicContentSize
Merge pull request #1925 from wordpress-mobile/issue/1915-jetpack-login-for-private-blog

Added sanity check when note's blog is 0
Merge pull request #1909 from wordpress-mobile/issues/1908-missing-featured-image-ipad

Skip fetching a new image from the cache and just copy instead.
Return out of method if topic is nil.
Merge pull request #1904 from wordpress-mobile/issues/1903-crash-nil-topic

Check for a nil topic before loading more.
Avoid redrawing cells when setting separator style.
Prevents CoreData Threading Exception
Implements FollowBlog Failsafe
Enables Dummy Notifications Pull To Refresh
NotificationsViewController: Loading matcher post on the mainMOC
ReaderPostService: calling failureBlock on error
Remove slicing data from btn-primary-tap asset

We're slicing in code anyway, and it was crashing for some reason

Fixes #1946
Merge pull request #1947 from wordpress-mobile/issue/1946-crash-imageNamed

Remove slicing data from btn-primary-tap asset
Merge pull request #1945 from wordpress-mobile/issues/1944-reader-post-details-crash

NotificationsViewController: Loading matcher post on the mainMOC
Merge pull request #1943 from wordpress-mobile/issues/1941-notifications-pull-to-refresh

Enables Dummy Notifications Pull To Refresh