ade info: Don't crash if an entry point has no icon

It is normal and expected for agent entry points to not have an icon.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Emanuele Aina <emanuele.aina@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D6858