Fix title update when changing active split view

Summary:
The DolphinTabPage::activeViewUrlChanged signal triggers the title
update in DolphinMainWindow, which sets the new title from the
`m_activeViewContainer` instance.

This means we need to notify the main window that the active view
changed before telling it that the current url changed.

BUG: 402641
FIXED-IN: 18.12.1

Reviewers: #dolphin, rizzitello, ngraham

Reviewed By: #dolphin, rizzitello, ngraham

Subscribers: rizzitello, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D17881