Exclude daemonized processes from Dolphin::attachToExistingInstance()

Summary:
`dolphin --daemon` does not have the `/dolphin/Dolphin_1` dbus path,
because it doesn't have any DolphinMainWindow.

Instead of working around this issue (as we did in D21666 and D25510),
just exclude these processes from the list of dbus instances checked by
`Dolphin::attachToExistingInstance()`.

CCBUG: 408244

Test Plan: Same test plan as in D21666 and D25510

Reviewers: #dolphin

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D26213