Hardened against null modpack builds from making it to the update
thread.

Signed-off-by: Dalton Pelc <daltonjpelc@gmail.com>
Fixed NPE in DynamicButton when the Icon was null. Needs a proper fix
where the icon is never null in the future.

Signed-off-by: Dalton Pelc <daltonjpelc@gmail.com>