GT Performance 1.3.4

Fixes a fatal error on sites running Query Monitor.

• The core-version rewrite on script_loader_src and style_loader_src no longer throws on a source that is not a string. Query Monitor applies both filters to dependency-only handles, whose src is false or null, and the string-typed DatabaseModule::assetVersion() threw a TypeError on null during shutdown, so every page that showed the Query Monitor panel ended in a fatal error. Any source that is not a string now comes back unchanged.