Use 0 for texcoord when not specified in vertex.

Can't find any other unprotected attributes (well, position, but that
should always be specified) so this fixes #5133.

Also fixes #5124 for me.
Merge pull request #5134 from unknownbrackets/gpu-minor

Use 0 for texcoord when not specified in vertex.
Oops, revert software transform breakage.

It will deal with getting the coords right, including in projection modes.