readAxivity()` fails with "object 'prevStart' not found" when only the final block is requested

[j262byuu]

readAxivity(start = n - 1, end = n), where n is the number of data blocks, fails with:

object 'prevStart' not found

That range asks for exactly one block, the final one. Any range starting earlier works, including a full read.

Reproducible example

library(GGIRread)

f <- system.file("testfiles/ax3_testfile.cwa", package = "GGIRread")
n <- (file.info(f)$size - 1024) / 512    # 145 data blocks

readAxivity(f, start = n - 3, end = n, progressBar = FALSE)   # ok, 362 rows
readAxivity(f, start = n - 1, end = n, progressBar = FALSE)   # Error: object 'prevStart' not found

Same on ax6_testfile.cwa, 283 blocks, start = 282, end = 283.

R 4.5.2, Windows.

Cause

Previously there's a check to prevent this, open 0522630 then search the following:

if (prevRaw$start >= start & pos <= nr & exists("prevStart") & exists("prevLength")) {

The later refactor removed this part

Why it may matter

If chunked processing leaves exactly one block in the final chunk, GGIRread will fail