[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

{F7575402}

Reviewers: #dolphin, elvisangelaccio

Subscribers: kfm-devel

Tags: #dolphin

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