Fix a spurious warning message

[johnsonjh]

Fixes a spurious warning message. In the case where pktctl is being used to control a pktd and/or pktwallet process not owned by the current user (but obviously on the same system), with any necessary RPC parameters specified as command-line options, then no warning message should be printed about being unable to read the RPC password from the users $HOME/.pktwallet directory - simply check to see if a password was specified before warning about it.

 » pktctl --notls --rpcuser=XXXX --rpcpass=XXXX --wallet getbalance
Warning: unable to get rpc password from path [/home/myuser/.pktwallet]
3031.8219427987933

With the patch:

 » pktctl --notls --rpcuser=XXXX --rpcpass=XXXX --wallet getbalance
3032.8619421137921

In this case, pktd is running as user pktd_ and pktwallet is running as user pktw_, and the user executing pktctl has neither a $HOME/.pktd or a $HOME/.pktwallet directory, nor is their existence necessary.