BUG: shap.plots.bar with cohorts dict throws UnboundLocalError

[thatlittleboy]

Bug report checklist

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of shap.
• I have confirmed this bug exists on the master branch of shap.
• I'd be interested in making a PR to fix this bug

Minimal Reproducible Example

import shap
import numpy as np

shap.plots.bar({
    "t1": shap.Explanation(
        values=np.random.randn(20, 5),
        base_values=0.5,
    ),
    "t2": shap.Explanation(
        values=np.random.randn(20, 5),
        base_values=0.5,
    ),
})

Issue Description

Run the above code snippet, an UnboundLocalError is thrown

Expected Behavior

No error is thrown

Installed Versions

The image above was with shap 0.41.0, but issue is reproducible with master (f77a5ae) as well.