Fix verification in robust buffer access tests

Fix verification in robust buffer access tests

Some buffer accesses to addresses less than 16 bytes away from the out
of bounds address where not considered potentially out of bounds, even
when there were out of bounds accesses in the same SPIR-V block.

Affects:

dEQP-VK.robustness.buffer_access.*:

Components: Vulkan

VK-GL-CTS issue: 1025

Change-Id: Ibcb61fb84cecc360d753ba5d3acc1f9d48169651