[AW NS] Fix crash: execute error callback and early-out when io_thread_client is null.

Make sure to prevent crashes when io_thread_client is null,
at the time when InterceptedRequest::Restart is called.
There is a small amount of crash reports, see
crbug.com/953584, which indicate this case could arise
in special cases.

BUG=953584,841556

Cq-Include-Trybots: luci.chromium.try:android_mojo
Change-Id: I958fa4d622125a2d54ef99aee83a598f4cf46be5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578751
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653652}
1 file changed