Cache bin: Add a debug method for init checking.

src/cache_bin.c

@@ -102,3 +102,8 @@ cache_bin_init(cache_bin_t *bin, cache_bin_info_t *info, void *alloc,
 	assert(cache_bin_ncached_get(bin, info) == 0);
 	assert(cache_bin_empty_position_get(bin, info) == empty_position);
 }
+
+bool
+cache_bin_still_zero_initialized(cache_bin_t *bin) {
+	return bin->cur_ptr.ptr == NULL;
+}