Reduce excessive error logging on empty songbook entries

[bensteUEM]

Executing main.py or it's respective update.ipynb from #22 creates excessive error logs

ERROR:SngFileHeaderValidationPart:Problem occurred with Songbook Fixing of Hast du schon gewusst.sng - kept original Songbook= ,ChurchSongID=

[bensteUEM]

• [ ] check why logger is triggered twice 2024-05-09T22:00:19+0200: [INFO|main:93] Starting validate_header_songbook(True) 2024-05-09T22:00:19+0200: [DEBUG|SngFileHeaderValidationPart:175] songbook_valid == False 2024-05-09T22:00:19+0200: [DEBUG|SngFileHeaderValidationPart:175] songbook_valid == False 2024-05-09T22:00:19+0200: [ERROR|SngFileHeaderValidationPart:183] Problem occurred with Songbook Fixing of Freude über Freude das Grab ist leer.sng - kept original Songbook= ,ChurchSongID= 2024-05-09T22:00:19+0200: [ERROR|SngFileHeaderValidationPart:183] Problem occurred with Songbook Fixing of Freude über Freude das Grab ist leer.sng - kept original Songbook= ,ChurchSongID=