[BUGFIX] DBAL sql_fetch_* must return boolean or array

If the end of a result set is reached some drivers produce NULL.
This must be changed into FALSE to be compatible with the
non-DBAL version of these functions.

Resolves: #57957
Releases: 6.2, 6.1
Change-Id: I664dd10735f88754c74e20ecd5c07fad5ef2b78d
Reviewed-on: https://review.typo3.org/29513
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert