Fix drawarrays-vertex-count GL_LINES test
Use the same + 0.5 trick as GL_LINE_LOOP / GL_LINE_STRIP. This fixes the test on both radeonsi and Nvidia 410.104 when using -fbo.
Use the same + 0.5 trick as GL_LINE_LOOP / GL_LINE_STRIP. This fixes the test on both radeonsi and Nvidia 410.104 when using -fbo.