Wrong `zkInput` generation

[krlosMata]

Summary of Bug

zkInputs are not properly generated when there is an exit transaction in L2 with 0 amount.

Expected Behavior

correct zkInputs generation

Additional Information:

When the exit tree is empty and a L2 exit transaction with amount 0 is performed, we do not create a new leaf in the exit tree. Thus, receiver leaf processor is not used and associated zkInputs fields should not matter expect for the tokenID2 that should match sender leaf unless the transaction is an L1 transaction or newExit (insert operation into the exit tree) transaction.

• Circuit checks could be found here
• Javascript zkInput generation recent fix

The suggested change to fix this issue would be:

• no leaf account sender exit tree + L2 exit amount = 0 --> signal newExit = 1 on zkInputs will solve tokenID2 check
• sender leaf already has an account on exit tree + L2 exit amount = 0 --> signal tokenID2 = tokenID1 to fulfill tokenID2 circuit check

[jeffprestes]

@Mikelle , could you please review it? I guess you have done this when you solved the issue related to "double exits"