bump buildkit 05766c5c21a1e528eeb1c3522b2f05493fe9ac47 (docker-18.09 branch)

- moby/buildkit#952 [18.09 backport] Have parser error on dockerfiles without instructions
  - backport of moby/buildkit#771 Have parser error on dockerfiles without instructions

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: a1d76e0585c498f5167b28b9909fd8c88fd3370d
Component: engine

components/engine/vendor.conf

@@ -26,7 +26,7 @@ github.com/imdario/mergo v0.3.6
 golang.org/x/sync 1d60e4601c6fd243af51cc01ddf169918a5407ca
 
 # buildkit
-github.com/moby/buildkit ed4da8b4a9661f278ae8433056ca37d0727c408b # docker-18.09 branch
+github.com/moby/buildkit 05766c5c21a1e528eeb1c3522b2f05493fe9ac47 # docker-18.09 branch
 github.com/tonistiigi/fsutil 2862f6bc5ac9b97124e552a5c108230b38a1b0ca
 github.com/grpc-ecosystem/grpc-opentracing 8e809c8a86450a29b90dcc9efbf062d0fe6d9746
 github.com/opentracing/opentracing-go 1361b9cd60be79c4c3a7fa9841b3c132e40066a7

components/engine/vendor/github.com/moby/buildkit/frontend/dockerfile/parser/parser.go

@@ -275,6 +275,11 @@ func Parse(rwc io.Reader) (*Result, error) {
 	if len(warnings) > 0 {
 		warnings = append(warnings, "[WARNING]: Empty continuation lines will become errors in a future release.")
 	}
+
+	if root.StartLine < 0 {
+		return nil, errors.New("file with no instructions.")
+	}
+
 	return &Result{
 		AST:         root,
 		Warnings:    warnings,