Error in writing character arrays with arbitrary size

[Artur-man]

Describe the bug

There seems to be an error when writing zarr arrays with character elements and arbitrary shape. I traced it here by debugging but couldn't really figure out:

pizzarr/R/zarr-array.R

Lines 633 to 648 in f84355d

	chunk_setitem = function(chunk_coords, chunk_selection, value, fields = NA) {
	# Reference: https://github.com/gzuidhof/zarr.js/blob/15e3a3f00eb19f0133018fb65f002311ea53bb7c/src/core/index.ts#L625
	if (private$order == "C" && self$get_ndim() > 1) {
	stop("Setting content for arrays in C-order is not yet supported.")
	}
	# Obtain key for chunk storage
	chunk_key <- private$chunk_key(chunk_coords)
	dtype_constr = private$dtype$get_typed_array_ctr()
	chunk_size <- compute_size(private$chunks)
	if (is_total_slice(chunk_selection, private$chunks)) {
	# Totally replace chunk

To Reproduce

mat <- array(rep("text", 545*689), dim = c(545, 689))
zarr.array <- pizzarr::zarr_open(store = "data/string_test.zarr", mode = "w")
zarr.array$create_dataset(name = "assay", data = mat, shape = dim(mat), dtype = "<S20")

Error

Error in buf[offset_i_start:offset_i_stop] <- raw_vec_i : 
  replacement has length zero

Environment:

• Release or git hash: f84355d
• Operating system: macOS Monterey v12.5.1
• R version: 4.3.1

[Artur-man]

This doesn't seem to be the case with other sizes:

mat <- array(rep("text", 100*100), dim = c(100, 100))
zarr.array <- pizzarr::zarr_open(store = "data/string_test.zarr", mode = "w")
zarr.array$create_dataset(name = "assay", data = mat, shape = dim(mat), dtype = "<S20")

<ZarrArray>
  Public:
    [: function (...) 
    [<-: function (...) 
    append: function (data, axis = 0) 

Also the problem doesn't occur with numeric arrays:

mat <- array(sample(1:20, 545*689, replace = TRUE), dim = c(545, 689))
zarr.array <- pizzarr::zarr_open(store = "data/pizzarr_test.zarr", mode = "w")
zarr.array$create_dataset(name = "assay", data = mat, shape = dim(mat))

<ZarrArray>
  Public:
    [: function (...) 
    [<-: function (...) 
    append: function (data, axis = 0)