`unreachable` triggered on weightless single-variant categorical

[llogiq]

Describe the bug WIth a categorical containing only one variant with a weight of 0, we happen upon an unreachable error.

To Reproduce Steps to reproduce the behavior:

1. Schema (if applicable)

   {
   "type": "array",
   "length": 1,
   "content": {
       "type": "object",
       "cat": {
           "type": "string",
           "categorical": {
               "empty": 0
           }
       }
   }
   }

2. See error

   thread 'main' panicked at 'internal error: entered unreachable code', /home/andre/projects/synth/core/src/schema/content/categorical.rs:82:9
   note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Expected behavior The single category should be used regardless of weight and also a warning about a single-variant categorical should be emitted.

Environment (please complete the following information):

• OS: any
• Version: 0.5.6