Stop reading from uninitialized memory

Stop reading from uninitialized memory

The compute pipeline statistics query test was accessing uninitialized
memory, which was causing an assert to randomly fail depending on what
tests were run beforehand.

Besides removing the access of the uninitialized memory, this change
also initializes the culprit memory in the base class to known invalid
values so that if another subclass is ever created with the same bug,
it will consistently assert.

VK-GL-CTS issue: 496
Components: OpenGL

Affects:

KHR-GL45.pipeline_statistics_query_tests_ARB.functional_compute_shader_invocations

Change-Id: Icc7478c98f617afee2fd53564473492fecd8836e