Correction of the siteRoot path

- Add a getOrElse to not only take a value that does not match the default.

Author: Dedelweiss

scaladoc/src/dotty/tools/scaladoc/Scaladoc.scala

@@ -207,7 +207,7 @@ object Scaladoc:
         classpath.get,
         bootclasspath.get,
         destFile,
-        siteRoot.nonDefault,
+        Option(siteRoot.withDefault(siteRoot.default)),
         projectVersion.nonDefault,
         projectLogo.nonDefault,
         projectFooter.nonDefault,