Bug 19671: Map itemtypes to hash for correct display in issues_stats.pl

Bug 19671: Map itemtypes to hash for correct display in issues_stats.pl

To test:
1 - Run the circulation wizard with itemtypes as columns, shelving
locations as rows - display on screen
2 - Note all itemtype values are blank
3 - Switch rows/columns - same issue
4 - Apply patch
5 - Re-run reports
6 - Itemtypes should display correctly

Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>