Arrow: Fix vectorized read of all-null DELTA-encoded Parquet pages

[raunaqmorarka]

Problem

Vectorized reads of Parquet V2 files crash with ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0 when a string/binary column page using DELTA_BYTE_ARRAY / DELTA_LENGTH_BYTE_ARRAY has zero non-null values (an all-null page).

at VectorizedDeltaEncodedValuesReader.lambda$readIntegers$3(VectorizedDeltaEncodedValuesReader.java:127)
at VectorizedDeltaEncodedValuesReader.readValues(VectorizedDeltaEncodedValuesReader.java:153)
at VectorizedDeltaEncodedValuesReader.readIntegers(VectorizedDeltaEncodedValuesReader.java:122)

Cause

An all-null page decodes to a length stream with totalValueCount == 0. readIntegers(0, …) allocates a zero-length array, but readValues always wrote firstValue into result[0].

Fix

Skip the first-value write when total == 0.

Test

Added a Spark vectorized-read test with all-null string and binary columns in a V2, dictionary-disabled file. It reproduces the crash before the fix and passes after.

[robinsinghstudios]

Eagerly looking forward to this getting merged :)