std: fix sendFileReading not accounting for buffer

Related to 1d764c1fdf04829cec5974d82cec901825a80e49

Test case provided by:

Co-authored-by: Kendall Condon <goon.pri.low@gmail.com>
889942a8b7Andrew Kelley committed on 10/8/2025, 11:45:38 PMparent4c27eef
3 files changedLine totals unavailable