"addpeer" command works with blank string

[swissrouting]

Example with CLN:

$ lightning-cli peerswap-addpeer
{
   "ReserveOnchainMsat": 0,
   "PeerAllowlist": [
      ""
   ],
   "AcceptAllPeers": false
}

Expected result: should see an error message like "peerswap-addpeer: missing argument for peer public key"

Actual result: successfully added an empty string to the PeerAllowlist.

[wtogami]

Good First Issue for someone who wants to get involved.

Suggested Fix:

• Validate the input is 66 characters, hex, lowercase.

Don't bother to deal with invalid line entries. People can delete them manually from their policy.conf.