message: doc: Document optional result fields in validateaddress
  Can be reviewed with --ignore-all-space --word-diff-regex=.
diff: static RPCHelpMan validateaddress()
  {
  - return RPCHelpMan{"validateaddress",
  + return RPCHelpMan{
  + "validateaddress",
  "\nReturn information about the given peercoin address.\n",
  {
  {"address", RPCArg::Type::STR, RPCArg::Optional::NO, "The peercoin address to validate"},
  @@ -52,7 +53,7 @@ static RPCHelpMan validateaddress()
  {RPCResult::Type::NUM, "witness_version", /* optional */ true, "The version number of the witness program"},
  {RPCResult::Type::STR_HEX, "witness_program", /* optional */ true, "The hex value of the witness program"},
  {RPCResult::Type::STR, "error", /* optional */ true, "Error message, if any"},
  - {RPCResult::Type::ARR, "error_locations", "Indices of likely error locations in address, if known (e.g. Bech32 errors)",
  + {RPCResult::Type::ARR, "error_locations", /*optional=*/true, "Indices of likely error locations in address, if known (e.g. Bech32 errors)",
  {
  {RPCResult::Type::NUM, "index", "index of a potential error"},
  }},
  