Fix indices in fuzzer.

There are a few places where an index is randomly generated, but the
max is incorrectly set to the size of the value not one less than
the size.

All of these occurrences have been fixed.

Bug: 306230574

Test: Ran fuzzer instance that failed, no longer fails.
Change-Id: I20dfbc19a0df9cb160f8c861e072f083e24a4fab