logo_name = None not handled properly, appears in sidebar

[sloria]

Related to the fix for #215 in 39cbbc1 .

I worked around the previous issue #215 by setting logo_name to None in html_theme_options:

html_theme_options = {
    "logo": "marshmallow-logo.png",
    "logo_name": None,
    # ...
}

but when I upgrade to alabaster 0.7.16, None appears in the sidebar

This is easily fixed by removing the logo_name setting, but the template should also properly handle None.

[picnixz]

PR welcome !