Fix builder for dockerfile template

Fix nil pointer dereference when getting the build options packages.

Signed-off-by: Han Verstraete (OpenFaaS Ltd) <[email protected]>

builder/build.go

@@ -59,13 +59,17 @@ func BuildImage(image string, handler string, functionName string, language stri
 		// this was never enforced.
 		langTemplate.Language = language
 
+		var tempPath string
 		if isDockerfileTemplate(langTemplate.Language) {
-			langTemplate = nil
-		}
-
-		tempPath, err := CreateBuildContext(functionName, handler, langTemplate, copyExtraPaths)
-		if err != nil {
-			return err
+			tempPath, err = CreateBuildContext(functionName, handler, nil, copyExtraPaths)
+			if err != nil {
+				return err
+			}
+		} else {
+			tempPath, err = CreateBuildContext(functionName, handler, langTemplate, copyExtraPaths)
+			if err != nil {
+				return err
+			}
 		}
 
 		if shrinkwrap {