Make the loading spinner toggle more explicit

Occasionally the loading spinner would stay visible after the tab finished loading. This change makes the toggle explicit so that it's always shown on beforeSend, and always hidden on complete.

Plus a bonus semi-colon eradication! 💥

Tagging this as 8.0 because I keep seeing it on GitLab.com which of course is running 8.0.x.

mentioned in issue #2572 (closed)

/cc @DouweM @patricio As discussed on Slack.

Reassigned to @DouweM

Status changed to merged

mentioned in commit 192dd58d

Picked into 8-0-stable.

Ughhhh, think this is still happening on gitlab.com even after we deployed 8.0.5.

Bah, I see the problem, will open another MR.

mentioned in merge request !1597 (merged)

mentioned in commit 7ad68523