Invalid waypoint styles use the missing texture instead of falling back to the default style

The missing texture should never be visible unless there is an issue with the currently active resource pack, however it’s possible to see it using the default resources using only two commands:

/summon minecraft:armor_stand ~ ~ ~ {attributes:[{id:waypoint_transmit_range,base:200}]}

/waypoint modify @n[type=minecraft:armor_stand] style set nonexistent

In such a case, the default icon should be used as a fallback texture; the missing texture should only appear if something is actually broken about the loaded packs.