Caused by 5621154185.
The Perpendicular Snap needs a `prev_co` to work.
But in `Snap With` `Closest` mode the `prev_co` is not calculated.
Thus, when isolated, the snap to Perpendicular is never done.
So this commit puts the `center_global` fallback back to `prev_co`.
Also, if `Snap Base Edit` is used when only the snap to
`Edge Perpendicular` is enabled. `Snap To` will be temporarily set to
`Vert`, `Edge`, `Face` and `Edge Midpoint`.