fix(compiler): handle null window.location.origin (#2813)

when using a data URI or file URI (#2582),
or when using iframe's `srcdoc`, the value for window.location.origin can be `null`.
in these particular cases, passing `null` to `new URL(url, null)` will throw the 
following error: "Failed to construct 'URL': Invalid base URL"

src/compiler/output-targets/dist-lazy/generate-system.ts

@@ -102,7 +102,8 @@ const getSystemLoader = async (
 
     var resourcesUrl = scriptElm ? scriptElm.getAttribute('data-resources-url') || scriptElm.src : '';
     var start = function() {
-      var url = new URL('${corePath}', new URL(resourcesUrl, window.location.origin));
+      // if src is not present then origin is "null", and new URL() throws TypeError: Failed to construct 'URL': Invalid base URL
+      var url = new URL('${corePath}', new URL(resourcesUrl, window.location.origin !== 'null' ? window.location.origin : undefined));
       System.import(url.href);
     };