Fixes subplots=True for geo=True and with by-statement

[hoxbro]

The second part (2/2) of the fix for https://discourse.holoviz.org/t/small-multiples-aka-facetted-plots/3760/2

This will make it possible to run (after holoviz/holoviews#5325 is merged):

import geopandas as gpd
import hvplot.pandas

countries = gpd.read_file(gpd.datasets.get_path('naturalearth_lowres'))
countries.hvplot(geo=True, by="continent", subplots=True)

Before fix (with holoviz/holoviews#5325):

After fix:

[jbednar]

Good catch!

[maximlt]

Added an xfail test in f30077c that was passing with holoviz/holoviews#5325.

We've discussed about holoviz/holoviews#5325 recently and the fix on the HoloViews side is likely going to be different. But that doesn't really matter for hvPlot, I think. @hoxbro do you see any reason not to merge this?

[hoxbro]

Nope. I would love to see this merged.

[maximlt]

Great thanks, merging then.