AutoExpand does not expand beyond non-default MaxExpansionDepth

[gathogojr]

Fixes OData/WebApi#2748

We set the default MaxExpansionDepth when the Validate method of the ODataQueryOptions object is called. The problem currently is that when the MaxExpansionDepth is overridden, for instance by assigning the value from the EnableQuery attribute ([EnableQuery(MaxExpansionDepth = 4)]), we call the Validate method before the AutoExpand navigation properties have been added to the SelectExpandQueryOption object. For that reason, the specified MaxExpansionDepth ends up not being respected for the auto-expanded navigation properties.

This pull request fixes that by calling ODataQueryOptions.AddAutoSelectExpandProperties prior to validating the SelectExpand query option.

[habbes]

Out of curiosity, 0 is not a valid max expansion depth?

[gathogojr]

@habbes What my investigation revealed is that if you set a MaxExpansionDepth of 0, that doesn't get applied - it defaults to configured MaxExpansionDepth of 2. The following won't prohibit expansion currently. That's the reason I used Context.ValidationSettings.MaxExpansionDepth > 0 in this PR to keep it consistent with the current behavior even as I follow up confirm if the current behavior is by design.
The following won't currently have the effect of preventing expansion:

[EnableQuery(MaxExpansionDepth = 0)]
public ActionResult<IEnumerable<Customer>> Get()
{
    return customers;
}