Otherwise there would be no clause with the dependencies needed for
ATEST set, so the GPU would get stuck.
Not needed on v7, as there shader_wait_dependency in the RSD will wait
for the dependencies before the shader starts.
Explicitly create a NOP instruction, as it is assumed that clauses
have a non-zero count of instructions in various places.
Fixes GPU timeouts in many applications, such as SuperTuxKart and
GZDoom.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11842>
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