Fix alternative criteria reordering when adding second alternative

[AAClause]

• Explicitly show sequence order controls when nbAlternatives > 1
• Use valid default index (nbAlternatives - 1) instead of out-of-range value
• Add bounds validation for criteriaIndex before setting selection

Fixes issue where entering data for a new alternative and changing its
order would cause the data to be lost, duplicating the existing alternative's
data instead.

Fixes #62