Fix: Download is started over and over when rotating the device

src/com/owncloud/android/ui/activity/FileDisplayActivity.java

@@ -1028,6 +1028,7 @@ OnSslUntrustedCertListener, EditNameDialogListener {
             }
             
             removeStickyBroadcast(intent);
+            mWaitingToPreview = null;
         }
 
         private boolean isDescendant(String downloadedRemotePath) {