We probably don't need it, but some code attempts to dereference
it so safer to have one then to start checking everywhere for
dereferences.
Fixes https://gitlab.com/kicad/code/kicad/issues/5353
- fix an issue when trying to enter a scale < 1.0: such a scale starts by 0, that was rejected by the filter)
- automatic clamp to user scale limits, to avoid many warnings to users.
- if the user scale is out of bounds, warn the user before trying to print, not when opening the dialog.
Wayne Stambaugh
Jeff Young
jean-pierre charras
qu1ck
Maciej Suminski