Fix crashes when remote accounts are null

app/src/main/java/fr/gouv/etalab/mastodon/helper/CrossActions.java

@@ -216,6 +216,9 @@ public class CrossActions {
             @Override
             protected void onPostExecute(Void result) {
                 List<Account> remoteAccounts = response.getAccounts();
+                if( response == null){
+                    return;
+                }
                 if( remoteAccounts != null && remoteAccounts.size() > 0) {
                     Intent intent = new Intent(context, ShowAccountActivity.class);
                     Bundle b = new Bundle();