[BUGFIX] Fix bug in HMENU special prev

This patch fixes a regression of patch #61721.
The array before this patch had numeric indexes and thus the first
one was not recognized in the prev menu.

Releases: master, 6.2
Resolves: #62482
Related: #61721
Change-Id: I2b05ffa3973fe7ca31b6e4ccd193d44718d1ec1a
Reviewed-on: http://review.typo3.org/34061
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>