api/handler/rpc: improvements and fixes (#1535)
api/handler/rpc: improvements and fixes (#1535)

* api/handler/rpc: fix empty body case
* api/handler/rpc: copy all request headers to metadata

Signed-off-by: Vasiliy Tolstov <c36af997645181f727020b1671b7c66b7a9c7a34@unistack.org>
myodc/go-micro,micro/go-micro