fix: uninitialized variable onions in makeseeds script

```
$ ./makeseeds.py protx.txt > nodes_main.txt
Traceback (most recent call last):
  File "DASH/contrib/seeds/./makeseeds.py", line 183, in <module>
    main()
  File "DASH/contrib/seeds/./makeseeds.py", line 167, in main
    for onion in onions:
                 ^^^^^^
UnboundLocalError: cannot access local variable 'onions' where it is not associated with a value
```

contrib/seeds/makeseeds.py

@@ -150,6 +150,7 @@ def main():
     else:
         mns = json.load(sys.stdin)
 
+    onions = []
     if len(sys.argv) > 2:
         with open(sys.argv[2], 'r', encoding="utf8") as f:
             onions = f.read().split('\n')