…ory even if Discard button is then pressed (#20236)

Fixes #20235

Fix-up of #20050
Summary of the issue:

When pressing apply in Magnifier settings panel, the values were not kept in memory. Thus, if dialog was then discarded, the initial values memorized when the dialog was opened were restored instead of the ones after Aply has been pressed.
Description of user facing changes:

When Mag settings dialog is discarded, the values of parameters present in the dialog when Apply was pressed are now restored as expected.
Description of developer facing changes:

N/A
Description of development approach:

Updated the *initially variables when settings panel is saved, i.e. when Apply or OK are pressed.
For OK, this has no impact since the dialog is closed.