text: Title: Invalid use of prefix in suite name is not validated
  Body: One can [force execution order](https://robotframework.org/robotframework/latest/RobotFrameworkUserGuide.html#test-suite-name-and-documentation) by naming suite files with prefix. 
  
  If user fails to give empty suite name (eg. `01__.robot`), the `name` attribute is missing from output.xml. Although rebot doesn't mind this (log and report just show empty suite name), it causes problems to other ecosystem tooling (eg. [Jenkins plugin](https://issues.jenkins.io/browse/JENKINS-69807))
  
  It would be nice if RF would consider this as invalid suite name.