assistant: work around libassistant crash

There is a bug in libassistant that would crash if starting a voice
session without any previous audio data. This works around the bug
until we can roll a real fix in.

Bug: 942268
Test: locally build and test with no crash
Change-Id: I7d5ba1246c789cb7fd4bfbfd540212f44ddc4f1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1524033
Reviewed-by: Yue Li <updowndota@chromium.org>
Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641290}
1 file changed