it used to live at icon-themes/galaxy/res/helpimg/starmath/ar_right.png

but got moved by...

commit 2f6f851a
Date:   Wed Sep 28 07:30:35 2016 +0200

    tdf#100015 (related) Move Math help icons to correct location

    So that they are actually packaged into the theme zip

and then removed by...

commit 38ded033
Date:   Mon Dec 12 15:11:13 2016 +0100

    Move help-specific images (the actual files) away from core

leaving this dialog missing its arrow image

Change-Id: I08127a823868d0b32b5f74bd5a7fb3fbfae95b28
Reviewed-on: https://gerrit.libreoffice.org/52023Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>