On indirect function calls, if the corresponding table entry is empty,
we cannot call {GetCodeFromStartAddress}. In that case, the signature
check will fail anyway, so perform the signature check first, and only
get the code object if the check succeeds.

R=mstarzinger@chromium.org

Bug: chromium:831463
Change-Id: Iead949e4c12502b1a2a3949db2dabab4a184a1e7
Reviewed-on: https://chromium-review.googlesource.com/1005005Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52542}