Extra vertices are added at the end of the vertex list when
processing a batch in order to avoid SIMD width overrun.
A single comparison can prevent us from processing these
vertices by disabling them in the stores and atomics mask.

This would fix the following tests:
dEQP-VK.synchronization.op.single_queue.*
when enabling the vertexPipelineStoresAndAtomics feature.

Note that these tests are affected because they wrongly
assume vertices won't be processed more than once. These
tests should still get fixed.

Bug b/140294254

Change-Id: I04185b899a9770537c3d10bcfd87e00e314582de
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36368
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>