Fixed rendering errors in complex particle system.

Fixed rendering errors in complex particle system.

We need to set the texture unit of the texture uniform as well, and we
might as well set all the texture units in initialize() since they're
constant.

Change-Id: Ifcc690351ec7d1db1d98ab74644e248ec43cd328
Reviewed-on: http://codereview.qt.nokia.com/1410
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>