When we decode operands of WebAssembly instructions, we do not use the
current pc but a pc of the instruction plus some offset. However, the
pc of the instruction + offset can become invalid in case of a decoder
error. Therefore we have to stop decoding operands explicitly in case
of an error.

R=clemensh@chromium.org

Bug: chromium:795131
Change-Id: I3b7b45782c71a70364adf930bee3e94a1be88fea
Reviewed-on: https://chromium-review.googlesource.com/832867
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50196}