build: refactor to avoid unneccessary nesting

Signed-off-by: Justin Chadwell <me@jedevc.com>

build/build.go

@@ -792,8 +792,7 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 	multiTarget := len(opt) > 1
 
 	for k, opt := range opt {
-		err := func(k string) error {
-			opt := opt
+		k, opt := k, opt
 		dps := m[k]
 		multiDriver := len(m[k]) > 1
 
@@ -816,17 +815,17 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 				for i, e := range so.Exports {
 					switch e.Type {
 					case "oci", "tar":
-							return errors.Errorf("%s for multi-node builds currently not supported", e.Type)
+						return nil, errors.Errorf("%s for multi-node builds currently not supported", e.Type)
 					case "image":
 						if pushNames == "" && e.Attrs["push"] != "" {
 							if ok, _ := strconv.ParseBool(e.Attrs["push"]); ok {
 								pushNames = e.Attrs["name"]
 								if pushNames == "" {
-										return errors.Errorf("tag is needed when pushing to registry")
+									return nil, errors.Errorf("tag is needed when pushing to registry")
 								}
 								names, err := toRepoOnly(e.Attrs["name"])
 								if err != nil {
-										return err
+									return nil, err
 								}
 								if ok, _ := strconv.ParseBool(e.Attrs["registry.insecure"]); ok {
 									insecurePush = true
@@ -1100,12 +1099,6 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opt map[s
 			}
 			return nil
 		})
-
-			return nil
-		}(k)
-		if err != nil {
-			return nil, err
-		}
 	}
 
 	if err := eg.Wait(); err != nil {