comdlg32: If a measurement system isn't specified use the default one and update the Flags field to reflect this.

This gives a minor performance improvement.

Based on a patch by Mike Ruprecht.

This also triggers page faults needed for DIB section access and write
watches.

This also triggers page faults needed for write watches.

This also triggers page faults needed for DIB section access.

comdlg32: We no longer need to update the dialog struct on exit as all of the information is up to date.