[SECURITY] XSS in Indexed Search statistics

Indexed Search statistics module is vulnerable to
persistent XSS attack injected by arbitrary frontend users.

Change-Id: Ieb87cfff20a5e49522a2410d24a3b2ae141535a0
Fixes: #31927
Releases: 6.0, 4.7, 4.6, 4.5
Security-Commit: 9aa89980af0db90bfc535f4858fc61036c3d8170
Security-Bulletin: TYPO3-CORE-SA-2012-004
Reviewed-on: http://review.typo3.org/13766
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader