[dolphin/search] Avoid unnecesary reloads on setSearchPath

Summary:
Check in setSearchPath() if the url passed is already the searchPath
This was causing an effect where reloading the same search URL results on buttons From Here/Everywhere toggling.
See D24422

Test Plan:
On your home folder press Ctrl-F several times
Buttons From Here/Everywhere should now not toggle each time

Reviewers: Dolphin, elvisangelaccio, meven, ngraham

Reviewed By: Dolphin, ngraham

Subscribers: kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D24449