RSX should discard draw calls with 0 weight in out-POS

[elad335]

This was discovered by accident while testing when I accidently initialized weight to 0, when I should have left it default-initialize to 1. The draw call was rendered on RPCS3 as if weight was 1, but was mysteriosly completely ignored on real PS3. Needs more investigation.

[kd-11]

Test case?
I already wrote a test case for this years ago, iirc RSX doesn't care what the weight it, there is no special treatment. In fact the vertex stage ATTRs are treated as if they're all the same and default to (0, 0, 0, 1);