message: don't try to decode invalid encoded ext keys
diff: @@ -167,7 +167,10 @@ public:
  K GetKey()
  {
  K ret;
  + if (vchData.size() == Size) {
  + //if base58 encouded data not holds a ext key, return a !IsValid() key
  ret.Decode(&vchData[0]);
  + }
  return ret;
  }
  