builder: several fixups from comments

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Upstream-commit: 305f73508022d0a3af65faa327aa798610969875
Component: engine

components/engine/builder/parser/parser.go

@@ -100,8 +100,7 @@ func Parse(rwc io.Reader) (*Node, error) {
 		}
 
 		if line != "" && child == nil {
-			for {
-				scanner.Scan()
+			for scanner.Scan() {
 				newline := strings.TrimSpace(scanner.Text())
 
 				if newline == "" {