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Also add another nullptr check for the AppConnectionHolder, similar to
crrev.com/c/1750467

Change-Id: Id6c8fc6a02aa21908fa89e6d624cd94cf099712f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752568Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686729}