[Request] sp_doc: Only show headers for object types present in database

[lowlydba]

Currently, all headers are always shown. If a database does not have any Views, it should not have a Views header included in the output.

• This requires checking for object type existence before building ToC and headers
• At least one unit test needs updating to account for the change in the minimum number of rows being output (as a proxy smoketest for results being returned correctly)