Fix broadcasts in Python UDFs when encryption is enabled

bin/pyspark --conf spark.io.encryption.enabled=true

...

bar = {"a": "aa", "b": "bb"}
foo = spark.sparkContext.broadcast(bar)
spark.udf.register("MYUDF", lambda x: foo.value[x] if x else "")
spark.sql("SELECT MYUDF('a') AS a, MYUDF('b') AS b").collect()

22/10/21 17:14:32 ERROR Executor: Exception in task 0.0 in stage 0.0 (TID 0)/ 1]
org.apache.spark.api.python.PythonException: Traceback (most recent call last):
  File "/Users/petertoth/git/apache/spark/python/lib/pyspark.zip/pyspark/worker.py", line 811, in main
    func, profiler, deserializer, serializer = read_command(pickleSer, infile)
  File "/Users/petertoth/git/apache/spark/python/lib/pyspark.zip/pyspark/worker.py", line 87, in read_command
    command = serializer._read_with_length(file)
  File "/Users/petertoth/git/apache/spark/python/lib/pyspark.zip/pyspark/serializers.py", line 173, in _read_with_length
    return self.loads(obj)
  File "/Users/petertoth/git/apache/spark/python/lib/pyspark.zip/pyspark/serializers.py", line 471, in loads
    return cloudpickle.loads(obj, encoding=encoding)
EOFError: Ran out of input