The func_index parameter passed to GetWasmFunctionNameFromTable can be
user-controlled through the CallSite constructor. Catch out-of-bounds
reads and return null as the function name in such cases.

This applies to the 5.3 branch and will be reverted on TOT in a bit.

BUG=632965

Review-Url: https://codereview.chromium.org/2199333002
Cr-Commit-Position: refs/heads/master@{#38276}