v0.31.6

What's Changed

• collections: stop reading values a columnarized record kept as undefined by @bbockelm in #294
• Repair an unreadable zone section, and count the repairs by @bbockelm in #295
• collections: test index candidates against the columns before rebuilding them by @bbockelm in #296
• collections: persist zone maps by attribute name by @bbockelm in #297

Full Changelog: v0.31.5...v0.31.6