While strictly speaking it is legal (though useless) to dynamically
create zero-length arrays with "new T[0]", UBSan does not like it,
so this CL avoids doing it. It fixes the error:

../../src/allocation.h:41:34: runtime error: constructor call on
address 0x... with insufficient space for an object of type 'unsigned char'

Bug: v8:3770
Change-Id: I5017767c59df0d8928f7493f92d2d04519083964
Reviewed-on: https://chromium-review.googlesource.com/c/1356902Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57984}