Fix Plasma applet printer job count
Summary: We were always showing the jobs for all printers, not for the currently open printer item
Test Plan:
- Have two printers setup (ideally one that is not connected)
- Print to the non connected printer
- See how without this patch the applet says "there's 1 job" for both printers
- See that with this patch it only says "there's 1 job" for the correct printer
Reviewers: dantti
Reviewed By: dantti
Subscribers: kde-utils-devel
Differential Revision: https://phabricator.kde.org/D10351