Only use gl_PointSize if GL_PROGRAM_POINT_SIZE is enabled
Fixes:
GTF-GL33.gtf32.GL3Tests.draw_elements_base_vertex.draw_elements_base_vertex_mode
GTF-GL33.gtf32.GL3Tests.draw_elements_base_vertex.draw_elements_base_vertex_count
Fixes:
GTF-GL33.gtf32.GL3Tests.draw_elements_base_vertex.draw_elements_base_vertex_mode
GTF-GL33.gtf32.GL3Tests.draw_elements_base_vertex.draw_elements_base_vertex_count