message: fix precision issues when rendering marker
diff: -float marker = floor(vMarker * 255.0);
  -if (marker != 0.0) {
  - if (mod(marker, 2.0) == 0.0) {
  +float marker = vMarker * 255.0;
  +if (marker > 0.1) {
  + if (mod(marker, 2.0) < 0.1) {
  gl_FragColor.rgb = mix(uHighlightColor, gl_FragColor.rgb, 0.3);
  } else {
  gl_FragColor.rgb = mix(uSelectColor, gl_FragColor.rgb, 0.3);
  