[G.NET] Allow to call multiple guard method on one If object

[mwereda]

Currently if one would like to guard variable against multiple conditions one need to write "check-line" for every condition:

Check.If(collection).IsNotEmpty();
Check.If(collection).HasItemsCountAtLeast(2);

It would be nice to split those two lines into one-liner:

Check.If(collection).IsNotEmpty().HasItemsCountAtLeast(2);

(above is not the best example but this shows the idea of problem)