allow multiple javadoc urls, e.g. for javafx (IDEA-98423)

java/idea-ui/src/com/intellij/openapi/roots/ui/configuration/libraryEditor/JavadocOrderRootTypeUIFactory.java

@@ -79,7 +79,7 @@ public class JavadocOrderRootTypeUIFactory implements OrderRootTypeUIFactory {
       specifyUrlButton.addCustomUpdater(new AnActionButtonUpdater() {
         @Override
         public boolean isEnabled(AnActionEvent e) {
-          return myEnabled && !isUrlInserted();
+          return myEnabled;
         }
       });
       toolbarDecorator.addExtraAction(specifyUrlButton);