[BUGFIX] Do not override array finisher options with empty values

Stop processing of array type finisher options, e.g. recipients, if
the flex form value is empty.

Resolves: #103867
Releases: main, 13.4, 12.4
Change-Id: I04cf14caf2fd18e9ff1c6842662736223330b4e8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84335


Reviewed-by: Daniel Goerz <daniel.goerz@b13.com>
Tested-by: Daniel Goerz <daniel.goerz@b13.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>