Added a NaN check in dotplot.py to avoid a deadloop in the matplot backend

[CalebG6]

Description

In the dotplot.py file I added a check to see if the values array has any NaNs and removed them locally if it does. Reasoning for this is because the backend matplot dot_plot function would get a NaN binwidth causing a deadloop.

from numpy import nan

arviz.plot_dot([0.81449801, 0.8748649 ,        nan,        nan,        nan], show=False)

The above plot uses this code
closes #2471

Checklist

• Follows official PR format
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

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📚 Documentation preview 📚: https://arviz--2483.org.readthedocs.build/en/2483/