multipart/form-data windows-1251

[UncleVic]

I have a problem with decoding messages in the charset windows-1251.
If a form contains charset=windows-1251, data can't be decoded correctly. After parsing a request a string will be corrupted.

My payload, for example. The tag <ErrorText> contains the charset windows-1251

POST /api/v1/events/providers/ipay HTTP/1.1
X-Forwarded-Proto: https
Connection: close
Content-Length: 673
Content-Type: multipart/form-data; charset=windows-1251; boundary=BS_20230321154848
User-Agent: BS_SOU_749

--BS_20230321154848
Content-Disposition: form-data; name="XML"

<?xml version="1.0" encoding="windows-1251" ?>
<ServiceProvider_Request>
  <DateTime>20230321154848</DateTime>
  <Version>1</Version>
  <RequestType>TransactionResult</RequestType>
  <ServiceNo>1</ServiceNo>
  <PersonalAccount>2gzD17a7MHFpnQGZmGag75</PersonalAccount>
  <Currency>933</Currency>
  <RequestId>6888</RequestId>
  <TransactionResult>
    <TransactionId>356624</TransactionId>
    <ServiceProvider_TrxId>2gzD17a7MHFpnQGZmGag75</ServiceProvider_TrxId>
    <CardTerminal>888888</CardTerminal>
    <ErrorText>Îïåðàöèÿ îòìåíåíà</ErrorText>
  </TransactionResult>
</ServiceProvider_Request>
--BS_20230321154848--

[UncleVic]

The Multer calls the Busboy constructor as Busboy({headers: req.headers, limits: limits, preservePath: preservePath}) after that, I have broken UTF8 string. If it be able to pass defParamCharset=latin1 we'll can decode a result string by iconv.decode(Buffer.from(stringFromBusboy, 'latin1'), 'win1251')

[Doc999tor]

I opened a PR for fixing this issue - #1210
Waiting for a review
@UncleVic maybe you could use the fork I until the PR is merged