[BUGFIX] indexed_search fix advanced search select boxes in extbase plugin

Fix missing labels for advanced search in extbase plugin.
- "Search in:"
- "From section:"
- "Order by:"
- "Category:"

Some language labels were renamed (the former names were never used).
It also fixes one uninitialized variable and wrong/missing doc comments

Resolves: #65817
Releases: master, 6.2
Change-Id: I519fa989ae5281be61105ceb05eb1438a5820469
Reviewed-on: http://review.typo3.org/37930


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>