minor: fix Context.ViewData ignored when nil is passed as view data on Context.View method

_examples/view/template_handlebars_0/main.go

@@ -4,6 +4,7 @@ import "github.com/kataras/iris/v12"
 
 func main() {
 	app := iris.New()
+	app.Logger().SetLevel("debug")
 
 	// Init the handlebars engine
 	engine := iris.Handlebars("./templates", ".html").Reload(true)
@@ -27,6 +28,21 @@ func main() {
 		ctx.View("example.html", viewData)
 	})
 
+	/* See context-view-data example: Set data through one or more middleware
+	app.Get("/view_data", func(ctx iris.Context) {
+		ctx.ViewData("author", map[string]string{"firstName": "Jean", "lastName": "Valjean"})
+		ctx.ViewData("body", "Life is difficult")
+		ctx.ViewData("comments", []iris.Map{{
+			"author": map[string]string{"firstName": "Marcel", "lastName": "Beliveau"},
+			"body":   "LOL!",
+		}})
+
+		ctx.Next()
+	}, func(ctx iris.Context) {
+		ctx.View("example.html")
+	})
+	*/
+
 	// Read more about its syntax at:
 	// https://github.com/aymerick/raymond and
 	// https://handlebarsjs.com/guide