Regression in Resource Spawner in Harmonic

[azeey]

Environment

• OS Version: Ubuntu 22.04
• Source or binary build? Binary, 8.5.0

Description

• Expected behavior: Resource spawner to work
• Actual behavior: Clicking on any of the models to download them fails with the error [GUI] [Wrn] [ResourceSpawner.cc:589] Download failed. Try again.. Trying to spawn the model fails with the error

  Error [SDF.cc:165] Tried to use callback in sdf::findFile(), but the callback is empty.  Did you call sdf::setFindCallback()?
  [GUI] [Wrn] [Spawn.cc:381] Only model or light entities can be spawned at the moment.

I bisected gz-fuel-tools and found that the regression started in https://github.com/gazebosim/gz-fuel-tools/pull/376

Steps to reproduce

1. gz sim -v4 empty.sdf
2. Add the ResourceSpawner gui plugin
3. Try to download or spawn any model

[mjcarroll]

I have managed to reproduce and bisect to the same location. Working on a fix now.