KateSessionManager: Limit the number of referenced jump list actions

Summary:

...to the number of defined actions

This fix the grumble...

  The desktop file "foobar/org.kde.kate.desktop" references the action
  "Session <checksum>" but doesn't define it

...when there are more than 10 sessions available

Test Plan:

• Ensure not to run a kate instance without this patch or you will see anymay the grumble
• Create more than 10 sessions
• Switch sessions and watch

Reviewers: Kate, cullmann

Reviewed By: Kate, cullmann

Subscribers: cullmann, kwrite-devel, Kate

Tags: Kate

Differential Revision: https://phabricator.kde.org/D16644