SPIIR produces too many low reduced chisq zerolags.

During O3, the reduced chisq was very biased towards small chisq.

A few different workarounds/fixes were tried, including:

• Adding a minimum threshold for chisq (#53)
• Excluding gaps from chisq calculation (#52)
• Fixing the cmbchisq calculation (#49)
• Bypassing Virgo (#31)

Most of the changes above are worth making separately, but this issue should track the overall science issue.