tdb2: rework check.c internal functions to return enum TDB_ERROR.

Of course, we leave the API the same, but percolate error codes all the
way back to tdb_check().

ccan/tdb2/private.h

@@ -453,7 +453,7 @@ unsigned int size_to_bucket(tdb_len_t data_len);
 tdb_off_t bucket_off(tdb_off_t ftable_off, unsigned bucket);
 
 /* Used by tdb_summary */
-size_t dead_space(struct tdb_context *tdb, tdb_off_t off);
+tdb_off_t dead_space(struct tdb_context *tdb, tdb_off_t off);
 
 /* io.c: */
 /* Initialize tdb->methods. */

ccan/tdb2/summary.c

@@ -113,8 +113,12 @@ static bool summarize(struct tdb_context *tdb,
 				+ rec_extra_padding(&p->u);
 			tally_add(chains, 1);
 			tally_add(extra, rec_extra_padding(&p->u));
-		} else
+		} else {
 			len = dead_space(tdb, off);
+			if (TDB_OFF_IS_ERR(len)) {
+				return false;
+			}
+		}
 		tdb_access_release(tdb, p);
 	}
 	if (unc)