Stop doing drawElements with count 0

[Aki-7]

zennist/src/icon-background.cc

Lines 67 to 69 in f984b9a

	GLsizei count = 0;
	base_technique_.DrawElements(
	GL_TRIANGLES, count, GL_UNSIGNED_SHORT, 0, &gl_element_array_buffer_);

There are a lot of warning in zen-remote-display-system like this.

...
01-20 01:29:32.852 20529 20560 E ZEN[Oculus]: GLES: unable to generate a triangle primitive because there are less than 3 vertices
01-20 01:29:32.852 20529 20560 W ZEN[Oculus]: GLES: unable to generate a triangle primitive because there are less than 3 vertices
01-20 01:29:32.852 20529 20560 D ZEN[Oculus]: GLES: unable to generate a triangle primitive because there are less than 3 vertices
01-20 01:29:32.852 20529 20560 E ZEN[Oculus]: GLES: unable to generate a triangle primitive because there are less than 3 vertices
...