Error: Problem with the local SSL certificate

Hi.

I have the following code that works like a charm on Linux using a P12 certificate:

```rust
extern crate curl;

use std::path::Path;

use curl::easy::SslVersion;
use curl::easy::{Easy, List};

fn main() {
let mut easy = Easy::new();
easy.url(
"https://nfe.sefaz.ba.gov.br/webservices/NFeConsultaProtocolo4/NFeConsultaProtocolo4.asmx",
)
.unwrap();
easy.verbose(true).unwrap();
let mut list = List::new();
list.append(
"SOAPAction: http://www.portalfiscal.inf.br/nfe/wsdl/NFeConsultaProtocolo4/nfeConsultaNF",
)
.unwrap();
list.append("Content-Type: application/soap+xml; charset=utf-8")
.unwrap();
easy.http_headers(list).unwrap();
easy.post_fields_copy(b"1CONSULTAR99999999999999999999999999999999999999999999").unwrap();
easy.ssl_verify_peer(false).unwrap();
easy.ssl_version(SslVersion::Tlsv12).unwrap();
easy.ssl_cert_type("P12").unwrap();
easy.ssl_cert(Path::new("/home/user/certificado.pfx"))
.unwrap();
easy.key_password("the-secret-password").unwrap();
easy.write_function(|data| {
println!("{}", String::from_utf8_lossy(data));
Ok(data.len())
})
.unwrap();
easy.perform().unwrap();
}

```

however, when I try to use the same example on Windows, it raises the following error:

```bash
* Trying 200.187.29.23:443...
* TCP_NODELAY set
* Connected to nfe.sefaz.ba.gov.br (200.187.29.23) port 443 (#0)
* schannel: Failed to get certificate location for C:\Users\user\Downloads\certificado.pfx
* Closing connection 0
* schannel: shutting down SSL/TLS connection with nfe.sefaz.ba.gov.br port 443
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { description: "Problem with the local SSL certificate", code: 58, extra: None }', src\libcore\result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
```

and I have been trying the following ways, but both fails:

```rust
...
easy.ssl_cert(Path::new("C:\\Users\\user\\Downloads\\certificado.pfx"))
.unwrap();
...
```

and

```rust
...
easy.ssl_cert(Path::new("C:/Users/user/Downloads/certificado.pfx"))
.unwrap();
...
```

it seems the library can't find the certificate location, maybe some encoding issue? I've tried the same code above in a C application and in cURL from command line and both worked like a charm.

TIA for any help!