remotedb/grpcdb: fix net.Listener leak in ListenAndServe

Uses Go's named return value feature to properly check and
ensure that if any error is encountered, that we properly
invoke .Close for the bound net listener inside of ListenAndServe.

Fixes tendermint#268

remotedb/grpcdb/server.go

@@ -16,11 +16,17 @@ import (
 // ListenAndServe is a blocking function that sets up a gRPC based
 // server at the address supplied, with the gRPC options passed in.
 // Normally in usage, invoke it in a goroutine like you would for http.ListenAndServe.
-func ListenAndServe(addr, cert, key string, opts ...grpc.ServerOption) error {
+func ListenAndServe(addr, cert, key string, opts ...grpc.ServerOption) (rerr error) {
 	ln, err := net.Listen("tcp", addr)
 	if err != nil {
 		return err
 	}
+	defer func() {
+		if rerr != nil {
+			_ = ln.Close()
+		}
+	}()
+
 	srv, err := NewServer(cert, key, opts...)
 	if err != nil {
 		return err