In the DATE42 algo, first pass must find the primitive that write the
bad alpha value. If depth test is fail, alpha value won't be written therefore
you mustn't keep the primitive id.
In theory to ensure 100% correctness, depth would need to be fully executed
(currently depth write is disabled). However it requires to copy the depth buffer.
It is likely bad for the perf.
Issue reported on DBZInfWorld
Gregory Hainaut
92553add8e