President Elector

Description
The RankedChoice.sol::selectPresident function does not validate that voters have ranked their candidates before selecting the president. There should be at least a minimum number of votes to be able to elect a new president; it would not be a democratic vote if a new president can be elected with only one voter.

Impact
There is a possibility that a president can be elected with only one vote.

Recommended mitigation
Add a validation to ensure each voter or at least a minimum number of voters has ranked candidates before the selection process begins.