dxSplitAddress returns incorrect error content if wallet is locked

[shrnkld]

Env: Blocknet core 4.3.3 public

Steps to reproduce:

1. via console enter cmd: dxsplitaddress BLOCK amount address
2. if the wallet is currently locked the error is returned as:

   {
   "error": "Bad Request address is invalid or not in the wallet for token BLOCK",
   "code": 1004,
   "name": "dxSplitAddress"
   }

Expected:

1. return:

   {
   "error": "Address split is not possible when the wallet is locked for token BLOCK. Please unlock the wallet and try again.",
   "code": ???,
   "name": "dxSplitAddress"
   }