Add glow::viewer::nothing, improve API safety
- Make
detail::raii_view_closerctor explicit - Add
viewer::nothing()allowing things like
auto v = (cond) ? viewer::rows() : viewer::nothing();detail::raii_view_closer ctor explicitviewer::nothing() allowing things likeauto v = (cond) ? viewer::rows() : viewer::nothing();merged
mentioned in commit 2131e664