Fix broken height_MoM RPC

[who-biz]

Output when calling after changes:

With height = -1 (converted to max height by chipsd)

./chips-cli -testnet height_MoM -1 
{
  "coin": "CHIPS",
  "height": 18261,
  "timestamp": 0,
  "error": "no MoM for height"
}

Without parameters (help text):

./chips-cli -testnet height_MoM 
error code: -1
error message:
height_MoM height
Calculates MoM for a given height, if it exists

Arguments:
1. height    (numeric, required) height for MoM calculation

Result:
{                            (json object)
  "coin" : "str",            (string) active coin
  "height" : n,              (numeric) requested block height
  "timestamp" : n,           (numeric) timestamp
  "depth" : n,               (numeric) MoMdepth
  "notarized_height" : n,    (numeric) height of last notarization
  "MoM" : "hex",             (string) MoM hash
  "kmdtxid" : "hex",         (string) txid from komodo
  "MoMoM" : "hex",           (string) MoMoM hash
  "MoMoMoffset" : n,         (numeric) MoMoffset
  "kmdstarti" : n,           (numeric) kmdstarti
  "kmdendi" : n              (numeric) kmdendi
}

[who-biz]

Note that not all of result fields will be provided in response, given certain conditions.