```
Avoid calculating the square root of negative zero, which can easily
happen on certain architectures when computing the population standard
deviation with a sample size of one, e.g.,
0.01 - (0.1 * 0.1) = -0.000000.
Avoid returning a NaN by capping the minimum possible variance value to
zero (positive).
In the future, maybe skip reporting statistics at all for a single
sample.
Reported by: Jenkins
```