Allow building buildx from source

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

src/util.ts

@@ -0,0 +1,8 @@
+export function isValidUrl(url: string): boolean {
+  try {
+    new URL(url);
+  } catch (e) {
+    return false;
+  }
+  return true;
+}