asan symbolize: Restore invalid utf-8 ignorance.

This was removed in
https://codereview.chromium.org/2818653003/diff/1/tools/valgrind/asan/asan_symbolize.py
but apparently tests do write invalid UTF-8 (maybe on Windows they write output in
the native codepage by default?).  Having stacks seems more important atm.

BUG=632047
TBR=vadimsh@chromium.org

Review-Url: https://codereview.chromium.org/2823563003
Cr-Original-Commit-Position: refs/heads/master@{#464730}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9d47da2334d77bd084aef8e0d5765a47967d449a
1 file changed