The streaming decoder computed the code section start from the passed
"offset". That offset is computed from the module offset *after* the
number of functions has been read. Hence 1 is subtracted, with the
comment:
// The offset passed to {ProcessCodeSectionHeader} is an error offset and
// not the start offset of a buffer. Therefore we need the -1 here.

That subtraction of 1 worked when the number of functions was encoded in
a 1-byte LEB, otherwise it was off.

This CL fixes the immediate issue of passing the right code offset. The
usage of the previously existing offset also seems wrong, and I will try
to clean that up in a follow-up CL.

R=ahaas@chromium.org
CC=szuend@chromium.org

Bug: chromium:1150303
Change-Id: I64bb2ececeb4749b7ba2096cd148ccb4079eca4f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2562383
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71503}