pmb.helpers.cli: set empty completer for no completion (MR 2055)

The default completer suggests files from the file system which we
really don't want here.
This can be tested with the 'Manufacturer' field for new devices.

Setting it to a custom lambda instead of None disables the completion
instead of using the default completer.

pmb/helpers/cli.py

@@ -68,7 +68,8 @@ def ask(args, question="Continue?", choices=["y", "n"], default="n",
 
         # Stop completing (question is answered)
         if complete:
-            readline.set_completer(None)
+            # set_completer(None) would use the default file system completer
+            readline.set_completer(lambda text, state: None)
 
         if lowercase_answer:
             ret = ret.lower()