With ANGLE the example in question does not show anything when drawing
with GL_POINTS. The value of gl_PointSize is undefined when not written
to. To be safe we set it to 1 properly in the vertex shader.

Change-Id: Ifb170568eccf1979f568e0e192ae3c2ce3282e80
Reviewed-by: Tomi Korpipää <tomi.korpipaa@digia.com>
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>