Using a git (libgit2) ssh remote URL with no login panics

[sqs]

Workaround is just to include the user in the URL, like ssh://git@github.com/sourcegraph/private-repo.git.

2014/10/21 13:43:35 http: panic serving 127.0.0.1:59114: runtime error: invalid memory address or nil pointer dereference
goroutine 20 [running]:
net/http.func·011()
    /usr/local/go/src/pkg/net/http/server.go:1100 +0xb7
runtime.panic(0x87df40, 0xd1ffb3)
    /usr/local/go/src/pkg/runtime/panic.c:248 +0x18d
github.com/libgit2/git2go.credentialsCallback(0x7ff5a3ffe8f8, 0x7ff598003b10, 0x0, 0x20, 0xc2080900f0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/libgit2/git2go/remote.go:135 +0xd4
github.com/libgit2/git2go._Cfunc_git_clone(0xc2081b8040, 0x7ff598000b50, 0x7ff598000b90, 0xc2081b6300, 0xc208192060)
    github.com/libgit2/git2go/_obj/_cgo_defun.c:405 +0x31
github.com/libgit2/git2go.Clone(0xc2081905d0, 0x2d, 0xc20819a320, 0x4c, 0xc2081a2380, 0x0, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/libgit2/git2go/clone.go:42 +0x1b9
github.com/sourcegraph/go-vcs/vcs/git.Clone(0xc2081905d0, 0x2d, 0xc20819a320, 0x4c, 0x101, 0xc2081a2100, 0x0, 0x0, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/sourcegraph/go-vcs/vcs/git/clone_update.go:55 +0x1de
github.com/sourcegraph/go-vcs/vcs/git.func·003(0xc2081905d0, 0x2d, 0xc20819a320, 0x4c, 0x101, 0xc2081a2100, 0x0, 0x0, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/sourcegraph/go-vcs/vcs/git/clone_update.go:30 +0x8b
github.com/sourcegraph/go-vcs/vcs.Clone(0xc2081a2006, 0x3, 0xc2081905d0, 0x2d, 0xc20819a320, 0x4c, 0x101, 0xc2081a2100, 0x0, 0x0, ...)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/sourcegraph/go-vcs/vcs/open_clone.go:103 +0x195
github.com/sourcegraph/vcsstore.(*service).Clone(0xc2080912c0, 0xc2081a2006, 0x3, 0xc2081a02a0, 0xc2081a2100, 0x0, 0x0, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/service.go:160 +0x107d
github.com/sourcegraph/vcsstore/server.(*Handler).serveRepoCreateOrUpdate(0xc20816af60, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/server/repo.go:40 +0x2ad
github.com/sourcegraph/vcsstore/server.*Handler.(github.com/sourcegraph/vcsstore/server.serveRepoCreateOrUpdate)·fm(0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000, 0x0, 0x0)
    /home/sqs/src/github.com/sourcegraph/vcsstore/server/handler.go:50 +0x56
github.com/sourcegraph/vcsstore/server.handler.ServeHTTP(0xc20816af60, 0xc20818c1e0, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    /home/sqs/src/github.com/sourcegraph/vcsstore/server/handler.go:74 +0x54
github.com/sourcegraph/vcsstore/server.(*handler).ServeHTTP(0xc20818c1f0, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    <autogenerated>:6 +0xae
github.com/sqs/mux.(*Router).ServeHTTP(0xc208034c80, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    /home/sqs/src/github.com/sourcegraph/vcsstore/Godeps/_workspace/src/github.com/sqs/mux/mux.go:98 +0x297
github.com/sourcegraph/vcsstore/server.(*Handler).ServeHTTP(0xc20816af60, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    /home/sqs/src/github.com/sourcegraph/vcsstore/server/handler.go:64 +0x49
net/http.(*ServeMux).ServeHTTP(0xc208032780, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    /usr/local/go/src/pkg/net/http/server.go:1511 +0x1a3
net/http.serverHandler.ServeHTTP(0xc208155260, 0x7ff5acdb60f8, 0xc2081b0000, 0xc20819e000)
    /usr/local/go/src/pkg/net/http/server.go:1673 +0x19f
net/http.(*conn).serve(0xc20817a700)
    /usr/local/go/src/pkg/net/http/server.go:1174 +0xa7e
created by net/http.(*Server).Serve
    /usr/local/go/src/pkg/net/http/server.go:1721 +0x313