[BUGFIX] Allow integers to be converted to objects

In TYPO3 CMS the identity of objects/ records are
integers (uids). Because of that, the persistent object
type converter should be able to convert integers to
objects, not only strings.

Releases: 6.2, 6.3
Resolves: #61292
Change-Id: I0b69295ae7adfdbe49cf19056614b984f34290c6
Reviewed-on: http://review.typo3.org/32592
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>