MS ABI: Fix logic bug in member pointer null test code

This code is trying to test if the pointer is *not* null.  Therefore we
should use 'or' instead of 'and' to combine the results of 'icmp ne'.
This logic is consistent with the general member pointer comparison code
in EmitMemberPointerComparison.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207815 91177308-0d34-0410-b5e6-96231b3b80d8