`StackOverflowException` when invoking `AddCollectionMappers()` twice.

[prochnowc]

When invoking AddCollectionMappers() twice all collection mapping operations throw a StackoverflowException.

public class UnitTest1
{
    public class DTO { }

    public class Model { }

    [Fact]
    public void Test1()
    {
        var config = new MapperConfiguration(c =>
        {
            c.AddCollectionMappers();
            c.AddCollectionMappers();
            c.CreateMap<Model, DTO>();
        });

        var mapper = new Mapper(config);
        mapper.Map<ICollection<DTO>>(new List<Model>() { new Model() });
    }
}

It would be really nice ifAddCollectionMappers() checks if the mapper is already registered. This is extremely useful when the application has many independent invocations of services.AddAutoMapper() in completely independent modules.

[lbargaoanu]

This project doesn't have a maintainer.

[prochnowc]

@lbargaoanu Can I open a PR to fix this problem?

[lbargaoanu]

No, there's nobody to review it.