proper parse (amending dd86d35375a7);

--- a/src/Pure/Build/build_manager.scala	Wed Jul 10 17:04:44 2024 +0200
+++ b/src/Pure/Build/build_manager.scala	Wed Jul 10 17:31:17 2024 +0200
@@ -17,6 +17,7 @@
   object Component {
     def parse(s: String): Component =
       space_explode('/', s) match {
+        case name :: Nil => Component(name)
         case name :: rev :: Nil => Component(name, rev)
         case _ => error("Malformed component: " + quote(s))
       }