[pc3/busyindicator] Hide when not running

Summary: When not running the indicator should be invisible. This matches the behaviour of the org.kde.desktop style.

Test Plan: Run KTrip with Plasma style. Open location search page. Indicator is only shown when actually loading things

Reviewers: Plasma, ngraham

Reviewed By: ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D28391