tree e633cdc85f3646cb83b51fc7c828fce2fae6313e
parent d248584b9090cff95ca0813e841c76e84ca201ce
author Avery Pennarun <apenwarr@gmail.com> 1365221017 -0400
committer Avery Pennarun <apenwarr@gmail.com> 1365221017 -0400

headgrid: handle situations where the stddev is zero.

Basically this is a "nulls and dots" graph.  nulls don't count toward
stddev, so we were dividing by zero.