Views: how to make an OR condition between filters and contextual filters
There is a module for that (albeit a sandbox module). Download Views arguments in filters. As it is a sandbox module you will have to use git.

With this module you add your contextual filter as a global null contextual filter. Then in your normal filter's section, you refer to your contextual filter via the format %N (%1 etc). In this way you bring your contextual filter down to the normal filter section in views, and you can now apply the conditional clauses there, as well as the other filter logic.