fix: Try all public keys

[tdakkota]

Updates #111.

[waybackarchiver]

I got an error after running this patch:

$ go run examples/auth/main.go 1001101111
Downloading public keys from https://git.io/JtImk, this can be insecure
panic: key can't be nil

goroutine 1 [running]:
github.com/xelaj/go-dry.PanicIf(...)
	/usr/local/src/go/pkg/mod/github.com/xelaj/[email protected]/errors.go:25
github.com/xelaj/mtproto/internal/keys.RSAFingerprint(0xc000453b60)
	/usr/local/src/go/src/github.com/replaced/mtproto/internal/keys/keys.go:27 +0x325
github.com/xelaj/mtproto.(*MTProto).makeAuthKey(0xc0000cd320)
	/usr/local/src/go/src/github.com/replaced/mtproto/handshake.go:42 +0x1a7
github.com/xelaj/mtproto.(*MTProto).CreateConnection(0xc0000cd320)
	/usr/local/src/go/src/github.com/replaced/mtproto/mtproto.go:153 +0x95
github.com/xelaj/mtproto/telegram.NewClient({{0xc00003e340, 0x38}, {0x76eb0b, 0x12}, {0xc00003e380, 0x3e}, {0x0, 0x0}, {0x0, 0x0}, ...})
	/usr/local/src/go/src/github.com/replaced/mtproto/telegram/common.go:85 +0x325
main.main()
	/usr/local/src/go/src/github.com/replaced/mtproto/examples/auth/main.go:33 +0x218
exit status 2

Maybe we can skip if publicKey is nil.

diff --git a/handshake.go b/handshake.go
index fe31a43..00cb3e6 100644
--- a/handshake.go
+++ b/handshake.go
@@ -39,6 +39,9 @@ func (m *MTProto) makeAuthKey() error { // nolint don't know how to make method
 
        var key *rsa.PublicKey
        for _, publicKey := range m.publicKeys {
+               if publicKey == nil {
+                       continue
+               }
                fp := keys.RSAFingerprint(publicKey)
                for _, b := range res.Fingerprints {
                        if uint64(b) == binary.LittleEndian.Uint64(fp) {

[quenbyako]

LGTM Thanks!