Fixed #24369 -- Prevented crash when `flush`ing before db migration

Thanks Thomas Tanner for the report.

django/core/management/commands/flush.py

@@ -46,6 +46,10 @@ class Command(BaseCommand):
         sql_list = sql_flush(self.style, connection, only_django=True,
                              reset_sequences=reset_sequences,
                              allow_cascade=allow_cascade)
+        if not sql_list:
+            raise CommandError(
+                "No commands to proceed with, maybe the database is still empty?"
+            )
 
         if interactive:
             confirm = input("""You have requested a flush of the database.