simplify the url parsing

Summary:
all urls need to have their ports stripped and text set, so de-duplicate
the shared code out of the conditional branches to prevent bugs from
making changes in one branch but not the other

Test Plan: saving and changing proxy settings continues to work

Reviewers: dfaure, apol

Reviewed By: apol

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D24559