substr() throws if pos == size

[AdmiralCurtiss]

For example:

    string_view x("abc");
    string_view y = x.substr(3);
    ASSERT_TRUE(y == "");

I would expect an empty string to be returned.
Compare https://en.cppreference.com/w/cpp/string/basic_string_view/substr

Note: See also bitwizeshift/string_view-standalone#3, same issue there.

[satoren]

Thank you for report.