server: fix NewHandlerOptions

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

server/options.go

@@ -303,6 +303,7 @@ type HandlerOptions struct {
 func NewHandlerOptions(opts ...HandlerOption) HandlerOptions {
 	options := HandlerOptions{
 		Context:  context.Background(),
+		Metadata: make(map[string]metadata.Metadata),
 	}
 
 	for _, o := range opts {