Refactor log_prob method in _MixtureBase class to handle negative inf…

…inity values in sum_log_probs (#1874)

numpyro/distributions/mixtures.py

@@ -149,7 +149,10 @@ def sample(self, key, sample_shape=()):
     def log_prob(self, value, intermediates=None):
         del intermediates
         sum_log_probs = self.component_log_probs(value)
-        return jax.nn.logsumexp(sum_log_probs, axis=-1)
+        safe_sum_log_probs = jnp.where(
+            jnp.isneginf(sum_log_probs), -jnp.inf, sum_log_probs
+        )
+        return jax.nn.logsumexp(safe_sum_log_probs, axis=-1)
 
 
 class MixtureSameFamily(_MixtureBase):