[BUGFIX] Avoid empty labels in EM configuration

Check if a given configuration option in the EM really has both
a headline and a text, before writing out an empty label.

Resolves: #57205
Releases: 6.2
Change-Id: I66c405f255b9bd6ba9b130088732984157cf4152
Reviewed-on: https://review.typo3.org/28665
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn