Consider: Prevent "no-op" calls to deposit altering functions?

[apbendi]

We should check and revert if the user attempts to make a deposit related call that is effectively a no-op. This would include:

• Staking 0 UNI
• Adding 0 UNI to an existing deposit
• Calling alter beneficiary with the same account
• Calling alter delegatee with the same account
• Withdrawing 0 UNI

This could help mitigate griefing attacks, but it's unclear it actually adds sufficient protection to be worthwhile. The attacker could still execute the attack extremely cheaply—gas costs remain by far the largest factor in dissuading such an attack.