[C++][Parquet] Fix crashes on invalid input (OSS-Fuzz)

[asfimport]

Fix more issues found by OSS-Fuzz.

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #26
• GitHub Pull Request #6848

_{Note: This issue was originally created as PARQUET-1835. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 6848
#6848