emscripten_fetch_unpack_response_headers returns header values with leading and trailing whitespace

[Aerlinger]

The emscripten_fetch_unpack_response_headers function in emscripten's fetch API will return header values with a single leading whitespace character ( ) and a trailing CRLF character (\r\n\).

This will apply all headers in the response.

Example: application/json\r\n will be returned when application/json is expected.

Code Example to reproduce:

char** response_headers =
          emscripten_fetch_unpack_response_headers(some_buffer);

if (response_headers) {
  for (int header_num = 0; response_headers[header_num];
       header_num += 2) {
    std::string key = response_headers[header_num];
    std::string value = response_headers[header_num + 1];
    
    cout << value << endl;  // e.g. output " application/json\r\n"
  }
  emscripten_fetch_free_unpacked_response_headers(response_headers);
}

Version of emscripten/emsdk:
5.0.8-git

[sbc100]

@brendandahl WDYT? Should be an easy fix I gues.. but would fixing this break any existing users.. hopefully not.