The immediate might not be 2 bytes from start of instruction, because
the opcode is leb encoded.

Bug: chromium:1143053
Change-Id: I3c514e771419470ce34e02d4faa24e9e59676aa6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2504852Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70828}