fix theme selector theme lookup

Review Request #129238 - Created Oct. 21, 2016 and submitted

Harald Sitter
knewstuff puts downloaded assets into subdirs like
`.local/share/kblocks/themes/brlublur-hotstuff-access/` which we found
correctly using a subdir iterator, but then failed to preserve the subdir
portion for later loading through KGameTheme in the same function.
to make sure KGameTheme can properly resolve the full path we need to pass
the desktop file path *relative* to data dir we found it in.

CHANGELOG: fix theme selector theme lookup

theme downloads correctly, then listed in selector, can be applied as theme, gets loaded, still loaded on app restart

Albert Astals Cid
Harald Sitter
Review request changed

Status: Closed (submitted)

Change Summary:

Submitted with commit 42897f89a03c2f46ff388df688f9a23675688908 by Albert Astals Cid on behalf of Harald Sitter to branch Applications/16.08.