Fix optimization when SO is used.

[ye-luo]

Proposed changes

The bug is very obvious and indicates no one ever tried this code path.
Closes #2914

5 steps of optimization, each with 2560 samples

                            LocalEnergy               Variance           ratio 
gs_vmc  series 0  -553.152087 +/- 0.124707   29.166798 +/- 0.884176   0.0527 
gs_vmc  series 1  -556.507485 +/- 0.078476   10.828886 +/- 0.676120   0.0195 
gs_vmc  series 2  -557.597605 +/- 0.100759   8.483432 +/- 0.307758   0.0152 
gs_vmc  series 3  -557.633509 +/- 0.075313   9.344380 +/- 0.768677   0.0168 
gs_vmc  series 4  -557.801874 +/- 0.054024   11.375561 +/- 1.200946   0.0204 

What type(s) of changes does this code introduce?

• Bugfix

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Bora

Checklist

• Yes. This PR is up to date with current the current state of 'develop'

[prckent]

I think the updates needed to support SO were simply not made ahead of people trying optimization with SO. Happy to see that the changes needed are quite small.