[dolphin/search] Fix search behavior when selecting "Your Files"

Summary:
Fix the search box forgetting the location where the user was previously searching into.

To do a search on "All Files" instead of setting the m_searchPath to $HOME, it checks the button state, so the "From Here" location is not lost.
As an added benefit, selecting "Your Files" when in a non-indexed folder will use the baloo search instead of a fully non-indexed search from $HOME.

This issue is the last remaining one of the series started with D24422, with the purpose of fixing the searchbox parsing and update.

Test Plan:

• Toggle between "From Here/Your Files" and navigate between locations
• The search box remembers the location and keeps a coherent state

Reviewers: Dolphin, elvisangelaccio

Subscribers: kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D24577