[BUGFIX] DataMapProcessor::synchronizeInlineRelations removes entities

[BUGFIX] DataMapProcessor::synchronizeInlineRelations removes entities

In case RelationHandler::readForeignField() is called with invalid UID
values for a parent record (e.g. zero, or non-numeric values), all records
might be selected if the database default value for a parent pointer field
is set to zero instead of NULL.

Besides that DataMapProcessor::synchronizeInlineRelations() uses the
mentioned RelationHandler method to resolve suggested and actually
persisted relations. The processing is adjusted to avoid invoking
RelationHandler using non-numeric parent pointer values.

Resolves: #81915
Releases: master, 8.7
Change-Id: I108501c69c9cdb732bb88526830f0f73f2d680af
Reviewed-on: https://review.typo3.org/53544
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>