`px.scatter(df, ..., render_mode="webgl")` fails when color column contains all `NaN`

[ChiQiao]

Code to reproduce the issue:

import pandas as pd
import numpy as np
import plotly.express as px

df = pd.DataFrame({"x": [0, 1], "y": [0, 1], "c": [np.nan, np.nan]})
px.scatter(df, x="x", y="y", color="c", render_mode="webgl")

Error:

There will be no issue for all the cases below:

1. remder_mode="svg"
2. "c": [None, None]
3. "c": [np.nan, 1] # i.e., not all NaN