add unhandled request auth type
add unhandled request auth type

fix

2020-02-18 11:43:57.396699 I | http: panic serving 172.28.0.43:50658: runtime error: invalid memory address or nil pointer dereference
goroutine 595 [running]:
net/http.(*conn).serve.func1(0xc0001fe3c0)
    /usr/lib/go/src/net/http/server.go:1767 +0x13b
panic(0x55c4e35f3820, 0x55c4e48b3c40)
    /usr/lib/go/src/runtime/panic.go:679 +0x1b6
github.com/chrislusf/seaweedfs/weed/s3api.(*IdentityAccessManagement).authRequest(0xc0004b84e0, 0xc000115900, 0xc0000bb650, 0x1, 0x1, 0x55c4e399d740)
    /go/src/github.com/chrislusf/seaweedfs/weed/s3api/auth_credentials.go:143 +0x11c
github.com/chrislusf/seaweedfs/weed/s3api.(*IdentityAccessManagement).Auth.func1(0x55c4e3994c40, 0xc0007808c0, 0xc000115900)
    /go/src/github.com/chrislusf/seaweedfs/weed/s3api/auth_credentials.go:111 +0x5e
net/http.HandlerFunc.ServeHTTP(0xc0004b87e0, 0x55c4e3994c40, 0xc0007808c0, 0xc000115900)
    /usr/lib/go/src/net/http/server.go:2007 +0x46
github.com/gorilla/mux.(*Router).ServeHTTP(0xc0004ba000, 0x55c4e3994c40, 0xc0007808c0, 0xc000115700)
    /root/go/pkg/mod/github.com/gorilla/mux@v1.7.3/mux.go:212 +0xe4
net/http.serverHandler.ServeHTTP(0xc00011e0e0, 0x55c4e3994c40, 0xc0007808c0, 0xc000115700)
    /usr/lib/go/src/net/http/server.go:2802 +0xa6
net/http.(*conn).serve(0xc0001fe3c0, 0x55c4e399d680, 0xc000894180)
    /usr/lib/go/src/net/http/server.go:1890 +0x877
created by net/http.(*Server).Serve
    /usr/lib/go/src/net/http/server.go:2927 +0x390

chrislusf/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs