Fix window icon not showing properly in launcher

See https://bugzilla.xamarin.com/show_bug.cgi?id=20886 and
https://jira.sil.org/browse/WS-53 for details.

Change-Id: Ie5f34519727dd04d7758a1af8d7fc513fbf97152
(cherry picked from commit 01b7bb554a561b158874bfd2e7a0a3e6014e4db2)