Crash when using `place_leaf` in a container

[fosterbrereton]

Eve crashes during eve_evaluate when the a container in the layout is placement: place_leaf (the default).

As a workaround, edit the end of eve_t::implementation_t::add_placeable to add the following logic when is_container_type is true:

if (!is_container_type) {
    parent->geometry_m.placement_m = place_leaf;
} else if (parent->geometry_m.placement_m == place_leaf) {
    parent->geometry_m.placement_m = place_row;
}

This will forcibly correct a container's placement to be something other than place_leaf.