GH-45257: [C++][Parquet] Fix Statistics<ByteArray> Cleanup handling

[mapleFU]

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

• GitHub Issue: [C++][Parquet] CleanStatistic for ByteArray might prune the zero-sized array #45257

[github-actions]

⚠️ GitHub issue #45257 has been automatically assigned in GitHub to PR creator.

[wgtmac]

When will we see this kind of data?

[wgtmac]

I guess the root cause is here:

arrow/cpp/src/parquet/statistics.cc

Lines 609 to 615 in 3b932bb

	if (!encoded_min.empty()) {
	PlainDecode(encoded_min, &min_);
	}
	if (!encoded_max.empty()) {
	PlainDecode(encoded_max, &max_);
	}
	has_min_max_ = has_min_max;

When both min_value and max_value exist but at least one of them is an empty string, min_ or max_ is not initialized.

Should we fix here instead of CleanStatistics above?

[wgtmac]

@pitrou @emkornfield WDYT?