Fix name display with null checks

tournaments/models/player_registration.py

@@ -85,10 +85,12 @@ class PlayerRegistration(TournamentSubModel):
             return "Anonyme"
         name = self.name()
         if (len(name) > 20 or forced) and self.first_name:
-            name = f"{self.first_name[0]}. {self.last_name}"
+            if self.first_name and len(self.first_name) > 0:
+                name = f"{self.first_name[0]}. {self.last_name}"
         if len(name) > 20 or forced:
             name_parts = self.last_name.split(" ")
-            name = f"{self.first_name[0]}. {name_parts[0]}"
+            if len(name_parts) > 0 and self.first_name and len(self.first_name) > 0:
+                name = f"{self.first_name[0]}. {name_parts[0]}"
         return name
 
     def clean_club_name(self):