Possible Bug: Lack check on counter range

Vulnerable File: `circuits/aes-gcm/aes-gctr-fold.circom`
commit: `65f823fc5606fca74440fb0de939ae07a3c39a80`

`counter` is computed as last_counter_num.out - 1 with no check that last_counter_num >= 1. If the 4-byte counter in step_in is 0, counter becomes -1 (i.e., a large field element), and index = counter*16 is a huge field value.