dabba: do not allow empty rpc server name.
dabba: do not allow empty rpc server name.

protobuf does not throw an error when binding to a socket with an empty
server name.
Therefore we need to catch it early and return EINVAL.

Signed-off-by: Emmanuel Roullit <e51ad7dcb99c77ecf30f537962c562ac80636eba@gmail.com>

eroullit/dabba,eroullit/dabba,eroullit/dabba,eroullit/dabba