Panic assertion failed: idx < self.len when casting DictionaryArrays with nulls

[alamb]

Describe the bug
When casting Dictionary --> StringArray the cast kernel panics with

thread 'main' panicked at 'assertion failed: idx < self.len', /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-buffer-44.0.0/src/buffer/boolean.rs:133:9

To Reproduce
Run this program:

[package]
name = "rust_arrow_playground"
version = "0.1.0"
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
arrow = {version = "44.0.0", default-features = false }

use std::{sync::Arc};

use arrow::{array::{StringArray, DictionaryArray, Int32Array, Array}, datatypes::{Int32Type, DataType}, buffer::{NullBuffer, BooleanBuffer}};




fn main() {
    let expected = vec![Some("a"), Some("a"), None, Some("c")];

    // Note that values must contain NULL to trigger this
    let values = StringArray::from(vec![Some("a"), Some("b"), Some("c"), None]);

    // third element is out of bounds in the values, but is also nulls so it should not cause issues
    let keys = Int32Array::from(vec![0, 0, 1000, 2]);
    let keys = set_null(keys, 2);

    let array = DictionaryArray::<Int32Type>::try_new(keys, Arc::new(values)).unwrap();

    let expected_array: DictionaryArray::<Int32Type> = expected.clone().into_iter().collect();
    assert_eq!(&array, &expected_array);

    // expand out to strings
    let new_array = arrow::compute::cast(&array, &DataType::Utf8).unwrap();
    let expected_array: StringArray = expected.clone().into_iter().collect();

    assert_eq!(new_array.as_ref(), &expected_array as &dyn Array);

    println!("Done!")
}


/// Sets the specific index to null and everything else non-null
fn set_null(keys: Int32Array, index: usize) -> Int32Array {
    let len = keys.len();

    let nulls: Vec<bool> = (0..len).map(|i| i != index).collect();
    let nulls = BooleanBuffer::from(nulls);

    let (_data_type, buffer, _old_nulls) = keys.into_parts();
    Int32Array::new(buffer, Some(NullBuffer::from(nulls)))

}

This results in

    Finished dev [unoptimized + debuginfo] target(s) in 0.81s
     Running `/Users/alamb/Software/target-df/debug/rust_arrow_playground`
thread 'main' panicked at 'assertion failed: idx < self.len', /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-buffer-44.0.0/src/buffer/boolean.rs:133:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/8ede3aae28fe6e4d52b38157d7bfe0d3bceef225/library/std/src/panicking.rs:593:5
   1: core::panicking::panic_fmt
             at /rustc/8ede3aae28fe6e4d52b38157d7bfe0d3bceef225/library/core/src/panicking.rs:67:14
   2: core::panicking::panic
             at /rustc/8ede3aae28fe6e4d52b38157d7bfe0d3bceef225/library/core/src/panicking.rs:117:5
   3: arrow_buffer::buffer::boolean::BooleanBuffer::value
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-buffer-44.0.0/src/buffer/boolean.rs:133:9
   4: arrow_buffer::buffer::null::NullBuffer::is_valid
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-buffer-44.0.0/src/buffer/null.rs:145:9
   5: arrow_buffer::buffer::null::NullBuffer::is_null
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-buffer-44.0.0/src/buffer/null.rs:151:10
   6: arrow_array::array::Array::is_null::{{closure}}
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-44.0.0/src/array/mod.rs:193:30
   7: core::option::Option<T>::map
             at /rustc/8ede3aae28fe6e4d52b38157d7bfe0d3bceef225/library/core/src/option.rs:1075:29
   8: arrow_array::array::Array::is_null
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-44.0.0/src/array/mod.rs:193:9
   9: arrow_array::array::Array::is_valid
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-array-44.0.0/src/array/mod.rs:210:10
  10: arrow_select::take::take_bytes
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-select-44.0.0/src/take.rs:404:16
  11: arrow_select::take::take_impl
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-select-44.0.0/src/take.rs:126:25
  12: arrow_select::take::take
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-select-44.0.0/src/take.rs:81:5
  13: arrow_cast::cast::unpack_dictionary
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-cast-44.0.0/src/cast.rs:3095:13
  14: arrow_cast::cast::dictionary_cast
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-cast-44.0.0/src/cast.rs:3074:14
  15: arrow_cast::cast::cast_with_options
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-cast-44.0.0/src/cast.rs:779:22
  16: arrow_cast::cast::cast
             at /Users/alamb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/arrow-cast-44.0.0/src/cast.rs:296:5
  17: rust_arrow_playground::main
             at ./src/main.rs:24:21
  18: core::ops::function::FnOnce::call_once
             at /rustc/8ede3aae28fe6e4d52b38157d7bfe0d3bceef225/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Expected behavior
The program should not panic and should print Done

Additional context
We found this error using internal data

@tustvold says he thinks the condition is backwards

for (i, offset) in offsets.iter_mut().skip(1).enumerate() {
            let index = indices.value(i).to_usize().ok_or_else(|| {
                ArrowError::ComputeError("Cast to usize failed".to_string())
            })?;

            if array.is_valid(index) && indices.is_valid(i) {