[Activities KCM] Fix patch to not delete default activity

Summary:
Patch referenced an id which didn't exist
BUG: 397887

Test Plan:
Had one activity, was disabled
Had two, both were enabled

Reviewers: Plasma, ngraham

Reviewed By: ngraham

Subscribers: ngraham, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D18159