Avoid using arg pointer.

The arg pointer is not really a struct cursor*, so skip the check altogether
and do the checks if CONSERVATIVE_CHECKS is defined.

Bug: 62350406

Test: Built art and ran test/testrunner/testrunner.py -b --host -t 137
Test: after removing the known failure. Verified before the fix, the test
Test: fails and after the fix, the test passes.
Change-Id: I4c9999e3292e469cb96080192027a2fc5ef9c857