std: fix sendFileReading not accounting for buffer

Related to 1d764c1fdf04829cec5974d82cec901825a80e49

Test case provided by:

Co-authored-by: Kendall Condon <goon.pri.low@gmail.com>
9ea4d9aa3bAndrew Kelley committed on 10/9/2025, 7:06:32 PMparent5c0ac90
2 files changedLine totals unavailable