expit of logistic variable gives log_prob 0.0

I'm trying to get the logprob of a expit-transformed logistic-distributed variable but it always returns zero:

```
import jax.random
from oryx.core.ppl import random_variable, log_prob
from jax.scipy.special import expit
import oryx.distributions as tfd

def simple_sample(key):
a = random_variable(tfd.Logistic(0., 1.))(key)
return expit(a)

x = simple_sample(jax.random.PRNGKey(0))
print(x) # 0.41845703
print(log_prob(simple_sample)(0.5)) # 0.0
print(log_prob(simple_sample)(x)) # 0.0
```
Versions:
jax-0.4.25
oryx-0.2.6

(Both a exp transformed logistic variable and a expit transformed normal variable seems to work, so there is something special about this combination)

Run the provided Python reproducer with jax, oryx.core.ppl.random_variable and log_prob, then compare it with the working exp-transformed logistic and expit-transformed normal cases mentioned in the report. Trace how Logistic and expit are handled by log_prob; done means the expit-transformed logistic variable produces the correct log probability for both 0.5 and the sampled value.

Written by the indexing model from the issue text.