[C++] if_else bug when using chunked string array with offsets

### Describe the bug, including details regarding any error messages, version, and platform.

I have a chunked array made of view/slices of the same array.

When I call if_else on that array, the results are wrong and it can results in strings that are not valid utf-8.

```python
import random

import pyarrow as pa
import pyarrow.compute as pc

sizes = [131072, 57066]
values = ['FOO', "BAR", "HELLO", "WOLRD", ""]

data = pa.array([random.choice(values) for _ in range(sum(sizes))])

inputs = pa.chunked_array(
[
data[:sizes[0]],
data[sizes[1]:]
]
)

results = pc.if_else(
pc.equal(inputs, ""),
pa.scalar(None, pa.string()),
inputs,
)

print(pc.unique(results).sort().to_pylist())
# this returns corrupted data, eg: ['\x00\x00\x00', '\x00\x00\x00\x00\x00', 'BAR', ...]
```

For context, I'm loading data from a parquet file, and replacing empty strings with nulls. This started happening when the size of the parquet file increased and data was chunked.

I've tested with pyarrow==16.0.0

### Component(s)

C++, Python