UI can already be non-existent

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

src/main/java/com/owncloud/android/ui/trashbin/TrashbinActivity.java

@@ -275,7 +275,9 @@ public class TrashbinActivity extends FileActivity implements TrashbinActivityIn
 
     @Override
     public void showError(int message) {
-        swipeListRefreshLayout.setRefreshing(false);
+        if (swipeListRefreshLayout != null) {
+            swipeListRefreshLayout.setRefreshing(false);
+        }
 
         if (emptyContentMessage != null) {
             emptyContentHeadline.setText(R.string.common_error);