[FIXED] Players can invite themselves to a party

[Xuri]

Tested using UOX3 0.98-4.0 and Client 6.0.12.3.

When using the /add command to invite someone to a party, players can target themselves to create a party of one. Parties of one are boring, and we should prohibit the ability to invite oneself to a party.

Testcase:
1. Log in
2. Type /add and press enter
3. Target yourself

[giwo]

Ok, resolved this, will commit the fix soon.