Fix private reading log errors

[jimchamp]

Closes #8917

Avoids error that occurs when a private reading log page is visited.

Also, sets default fall-back value of MyBooksTemplate.counts to an empty dict. This doesn't fix anything, but should give developers an indication, with a cursory glance, that this property is meant to be a dict.

Technical

Today, whenever a private reading log page is visited, the default mb.counts value is an empty list. The reading log view handler attempts to set the values of KEYS_TITLES by accessing mb.counts with a key, which causes an error when mb.counts is a list. The PR sets KEYS_VALUES inside of the conditional that checks if the page is viewable, avoiding the error altogether.

Testing

1. Open a private browser window, and navigate to a private reading log page. Ensure that you are redirected to the expected profile page.
2. Navigate to a public reading log page. Ensure that the expected reading log page is rendered without error.

Screenshot

Stakeholders

[cdrini]

Might be best to pull the raise to the top and flip the if statement. That makes it into the common "bail early" pattern which we tend to use a lot. Otherwise tested on testing and lgtm!

[mekarpeles]

tested, works!