revert Platform access to get active shell.

Change-Id: I93810712842e9f771baf7434d09ea84d8799f716
diff --git a/org.eclipse.scout.rt.ui.swt/src/org/eclipse/scout/rt/ui/swt/AbstractSwtEnvironment.java b/org.eclipse.scout.rt.ui.swt/src/org/eclipse/scout/rt/ui/swt/AbstractSwtEnvironment.java
index 0757d73..ed9a3de 100644
--- a/org.eclipse.scout.rt.ui.swt/src/org/eclipse/scout/rt/ui/swt/AbstractSwtEnvironment.java
+++ b/org.eclipse.scout.rt.ui.swt/src/org/eclipse/scout/rt/ui/swt/AbstractSwtEnvironment.java
@@ -873,8 +873,7 @@
   }
 
   public IForm findActiveForm() {
-    Shell activeShell = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell();
-//    Shell activeShell = getDisplay().getActiveShell();
+    Shell activeShell = getDisplay().getActiveShell();
     if (activeShell == null) {
       return null;
     }