clarified count_file;

--- a/src/Pure/PIDE/headless.scala	Mon Oct 14 22:34:33 2019 +0200
+++ b/src/Pure/PIDE/headless.scala	Mon Oct 14 22:37:43 2019 +0200
@@ -92,7 +92,7 @@
       def finished: Load_State = Load_State(Nil, Nil, 0)
 
       def count_file(name: Document.Node.Name): Long =
-        name.path.file.length
+        if (loaded_theory(name)) 0 else name.path.file.length
     }
 
     private case class Load_State(