Reorder MergeRequestTabs constructor

The tab was being activated before we set the [commits|diffs]Loaded variable, so even when the /diffs route is accessed directly, like from the "Side-by-side" link, the tab was being loaded from its default source.

Fixes #1887 (closed)

Added 2 commits:

• d2b5c3f6 - Trigger sticky_kit:recalc when diffs are pre-loaded
• e14d517b - Fix merge request diff features

Reassigned to @dzaporozhets

@dzaporozhets Good to go.

mentioned in commit 06ab7d89

Status changed to merged