[BUGFIX] Fix TypeError in AssetCollector if identifier is numeric

Although registered as "string" argument in the ViewHelper, an incoming
string that is_numeric() is cast to an integer, leading to a TypeError.

Resolves: #90873
Releases: master
Change-Id: Ic2b0cd8df1a75c46a22a605d6f7e3a0e2438a1d6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63993


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>