Fix regression w/ PartRequest (attachment loading)

* D'oh!

Bug: 4081610
Bug: 4084030
Change-Id: I99747d570b9487770f1028215b493b28707012ac
diff --git a/src/com/android/exchange/PartRequest.java b/src/com/android/exchange/PartRequest.java
index 2cc322d..23b4add 100644
--- a/src/com/android/exchange/PartRequest.java
+++ b/src/com/android/exchange/PartRequest.java
@@ -31,7 +31,7 @@
     public final String mLocation;
 
     public PartRequest(Attachment _att, String _destination, String _contentUriString) {
-        super(_att.mId);
+        super(_att.mMessageKey);
         mAttachment = _att;
         mLocation = mAttachment.mLocation;
         mDestination = _destination;