try to fix hang on index blob merge on shutdown

http://mantis.tokeek.de/view.php?id=505
It happens but not able to reproduce. This change makes sure terminate signal is catched at end of currently running merge jobs

source/net/yacy/kelondro/rwi/IODispatcher.java

@@ -69,8 +69,8 @@ public class IODispatcher extends Thread {
     }
 
     public void terminate() {
+        this.terminate = true; // asure current run() loop will termiate
         if (this.termination != null && this.controlQueue != null && isAlive()) {
-            this.terminate = true;
             this.controlQueue.release();
             // await termination
             try {