reftable/block: use size_t to track restart point index

The function `block_reader_restart_offset()` gets the offset of the
`i`th restart point. `i` is a signed integer though, which is certainly
not the correct type to track indices like this. Furthermore, both
callers end up passing a `size_t`.

Refactor the code to use a `size_t` instead.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/block.c

@@ -326,9 +326,9 @@ int block_reader_first_key(const struct block_reader *br, struct strbuf *key)
 	return 0;
 }
 
-static uint32_t block_reader_restart_offset(const struct block_reader *br, int i)
+static uint32_t block_reader_restart_offset(const struct block_reader *br, size_t idx)
 {
-	return get_be24(br->restart_bytes + 3 * i);
+	return get_be24(br->restart_bytes + 3 * idx);
 }
 
 void block_iter_seek_start(struct block_iter *it, const struct block_reader *br)