Editor / Remove extra space on mandatory add action

[fxprunayre]

If button label is not empty, do not add unneeded space. This was more visible on mandatory elements.

Checklist

• I have read the [contribution guidelines](https://github.com/geonetwork/core-geonetwork/blob/main/CONTRIBUTING.md
• Pull request provided for main branch, backports managed with label
• Good housekeeping of code, cleaning up comments, tests, and documentation
• Clean commit history broken into understandable chucks, avoiding big commits with hundreds of files, cautious of reformatting and whitespace changes
• Clean commit messages, longer verbose messages are encouraged
• API Changes are identified in commit messages
• Testing provided for features or enhancements using automatic tests)
• User documentation provided for new features or enhancements in mannual
• Build documentation provided for development instructions in README.md files
• Library management using pom.xml dependency management. Update build documentation with intended library use and library tutorials or documentation

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

The version of Java (11.0.20.1) you have used to run this analysis is deprecated and we will stop accepting it soon. Please update to at least Java 17.
Read more here

[josegar74]

Code change looks fine, although not tested as not very clear how to configured a label to display in the add elements.

[fxprunayre]

Code change looks fine, although not tested as not very clear how to configured a label to display in the add elements.

You can test it with a non existing mandatory element eg. remove the abstract in XML view and check the + in full view