[BUGFIX] Fix behavior of revExplode if delimiter not found

If the given delimiter is not found in the given string
GeneralUtility::revExplode() will return an array with a single element
containing the unexploded string.

Resolves: #55838
Releases: 6.2
Change-Id: I1146552a625a8057be86b2745febf808638a290c
Reviewed-on: https://review.typo3.org/27524
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn