Check static event shape rather than dynamic.

This helps with tf.function.

PiperOrigin-RevId: 299952015
Change-Id: I71f4b851a4ed5316cd5aa6d3757f2dcdd59b87b7

Author: Johannes Ballé

tensorflow_compression/python/entropy_models/continuous_base.py

@@ -62,7 +62,7 @@ def __init__(self, prior, coding_rank, compression=False,
         less precision, by using a Golomb-like code.
       range_coder_precision: Integer. Precision passed to the range coding op.
     """
-    if not prior.is_scalar_event():
+    if prior.event_shape.rank:
       raise ValueError("`prior` must be a (batch of) scalar distribution(s).")
     super().__init__()
     self._prior = prior