ethdb/leveldb: check iterator error in Database.DeleteRange (#32384)

Add missing it.Error() check after iteration in Database.DeleteRange to
avoid silently ignoring iterator errors before writing the batch.

Aligns behavior with batch.DeleteRange, which already validates iterator
errors. No other functional changes; existing tests pass (TestLevelDB).

ethdb/leveldb/leveldb.go

@@ -233,6 +233,9 @@ func (db *Database) DeleteRange(start, end []byte) error {
 			return err
 		}
 	}
+	if err := it.Error(); err != nil {
+		return err
+	}
 	return batch.Write()
 }