Core: Provide a better error message if only weights.yaml is provided with players: 0 (#2227)

Generate.py

@@ -127,6 +127,13 @@ def main(args=None, callback=ERmain):
                 player_id += 1
 
     args.multi = max(player_id - 1, args.multi)
+
+    if args.multi == 0:
+        raise ValueError(
+            "No individual player files found and number of players is 0. "
+            "Provide individual player files or specify the number of players via host.yaml or --multi."
+        )
+
     logging.info(f"Generating for {args.multi} player{'s' if args.multi > 1 else ''}, "
                  f"{seed_name} Seed {seed} with plando: {args.plando}")