Previously, when checking whether the gradient was required to determine
whether to apply hooks, only the existance of a grad_fn of the input was
checked. This was insufficient, since the first layer input may not have
a grad_fn yet, but still require a gradient. Now, the input is checked
for requires_grad instead, since a grad_fn is not needed, because of the
subsequent Identity.apply.
It is still sufficient to check for grad_fn for the output, since the
output will always have a grad_fn if a gradient is required.
Previously, when checking whether the gradient was required to determine whether to apply hooks, only the existance of a grad_fn of the input was checked. This was insufficient, since the first layer input may not have a grad_fn yet, but still require a gradient. Now, the input is checked for requires_grad instead, since a grad_fn is not needed, because of the subsequent
Identity.apply. It is still sufficient to check for grad_fn for the output, since the output will always have a grad_fn if a gradient is required.Closes #44