tools/squashfs4: fix rare data corruption issue

tools/squashfs4: fix rare data corruption issue

There is a chance that the squashfs4 tool may create a broken image
under certain conditions. Backport the fix from upstream to address
this issue.

Report: https://forum.openwrt.org/t/bug-squashfs4-tools-4-7-4-create-corrupted-image/244894
Fixes: 64432358e098 ("tools/squashfs4: update to 4.7.3")
Reported-by: Oleg S <remittor@gmail.com>
Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/21458
Signed-off-by: Robert Marko <robimarko@gmail.com>