[MCPE-183991] Specifying a nonexistent material in a client entity definition crashes the game

The bug

If an entity tries to render a material that does not exist, the game crashes.

How to reproduce

1. Download and open the attached world

Expected behavior
No crash, entity renders as invisible or something.

Observed behavior
Game instantly crashes before the world can even load.

Notes
The relevant entity file is entity/shooter1.json. It's been duplicated here for convenience:

{
   "format_version": "1.20.0",
   "minecraft:client_entity": {
      "description": {
         "identifier": "test:shooter1",
         "materials": {
            "default": "blahnotreallol"
         },
         "textures": {
            "default": "textures/entity/cow/cow"
         },
         "geometry": {
            "default": "geometry.cow"
         },
         "render_controllers": [
            "controller.render.default"
         ]
      }
   }
}