Allow default event sources that don't start with an alpha character

Visual Studio creates default event sources whose names start with an
underscore.

Fixed by ernest@eis.ru. [rt.cpan.org #43574]
Use '{' instead of non-alpha to determine if something is a CLSID or IID

Suggested by Daniel Dragan <bulkdd@cpan.org> in a comment of [rt.cpan.org #43574].