fixed critical bug that jumbled up texture coordinates on some hardware.

* texture coordinate stride was set incorrectly to 3 (needs to be 2 of course) - whilst the majority of cards and drivers is forgiving in this case, this leads to pretty nasty texture coordinate bugs on some hardware.
* thanks to @jacres for pointing out this bug and helping to track it down=)

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>