micro-clarification in API doc null vs. zero
Fix optimization for max hyperrange not being used
Small modification in hyperspace duration balance

This is just da530455935835eca69667e3b612897d573a5e3e reapplied. It was lost
due to #1719 not being updated after that commit was merged.
Win32 doesn't have isnan(). C++11 does have std::isnan() though :)