[SPARK-12300] [SQL] [PYSPARK] fix schema inferance on local collections

Current schema inference for local python collections halts as soon as there are no NullTypes. This is different than when we specify a sampling ratio of 1.0 on a distributed collection. This could result in incomplete schema information.

Author: Holden Karau <holden@us.ibm.com>

Closes #10275 from holdenk/SPARK-12300-fix-schmea-inferance-on-local-collections.