In Icc240d5c8c04198640eb118565ea99f10ba27466 we introduced support for
writing files > 255 bytes by splitting the write into multiple chunks.
However, at the same time, that commit broke support for writing data at
non-zero offsets. Unfortunately, this is used extensively within
pySim-prog e.g. for writing K + OP/OPc data to sysmoISIM-SJA2 and sysmoUSIM-SJS1
cards.
This commit fixes the related problem.
Change-Id: Ie1aeaab29701946233ed73db3331039690d695da
Fixes: Icc240d5c8c04198640eb118565ea99f10ba27466
Closes: OS#5254