ImmediateInterpreter: Add crash checks for SortFingersByProximity

This function is crashing occasionally. I'm not sure why,
unfortunately, but this should at least avoid the crash. In my tests,
there is no negative side effect of these checks.

BUG=chromium:341247
TEST=Manually tested, used mtstat to try to repro (and unfortunately
didn't work). Unittests pass.

Change-Id: Ie90d6caf35fa73c43d87609ab08d5cf1d502dc89
Reviewed-on: https://chromium-review.googlesource.com/185234
Reviewed-by: Dennis Kempin <denniskempin@chromium.org>
Commit-Queue: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
1 file changed