Local autosave may throw error for suspend() and resume()

[azaozz]

In (the rare) case when the browser doesn't support sessionStorage, wp.autosave.local returns early and doesn't expose any methods. Plugins that are trying to use any of them would trigger an error unless they check specifically if the method exists.

Ideally it should always expose the methods and they should return early when the browser doesn't support sessionStorage.

[azaozz]

In 29192:

Autosave: always expose the wp.autosave.local methods, fixes #28924.