Make sure we're getting an object instead of a collection on Asset API for model_id

[snipe]

We were being haunted by a bug that was returning Property [fieldset] does not exist on this collection instance via API for some users. In introspecting their payloads, they were sending an array instead of an int as the model ID. While we validate this at the asset level, when we're searching for the model ID., laravel can sometimes "helpfully" return a collection instead of a specific object. This is all well and good, but in this case we want only one model_id's results.

[what-the-diff]

PR Summary

• Refinement to Model Retrieval in Asset Storage
  The way we obtain the 'model' in the function for storing Assets has been upgraded. Initially, the 'find' function was used to get the 'model_id' from the request. But now, it's been changed to a more targeted approach. We're now using a 'where' clause that precisely gets the 'model_id' equal to the one in the request, and only the first match is returned. This enhances the efficiency and pinpoint accuracy when retrieving the 'model' information.