When starting a navigation operation that uses `Auto Depth` or
`Orbit Around Selection` the value of `#RegionView3D::dist` is modified
to match the distance from the new pivot.
This value was incorrect when the pivot was behind the viewer.
In these cases `dist` is negative.
This commit, in addition to fixing `dist`, also limits the execution of
this code to only when `Auto Depth` is used.
Pull Request: https://projects.blender.org/blender/blender/pulls/122795
2cb8b4b7f7