exceptions: assign result = null properly;

--- a/lib/jedit/plugin/isabelle/IsabellePlugin.scala	Wed Jan 23 22:57:09 2008 +0100
+++ b/lib/jedit/plugin/isabelle/IsabellePlugin.scala	Wed Jan 23 22:57:11 2008 +0100
@@ -110,8 +110,8 @@
           try {
             result = IsabellePlugin.isabelle.results.take.asInstanceOf[IsabelleProcess.Result]
           } catch {
-            case _: NullPointerException => null
-            case _: InterruptedException => null
+            case _: NullPointerException => result = null
+            case _: InterruptedException => result = null
           }
           if (result != null) {
             System.err.println(result)   // FIXME