Writing some special character in label will cause Cesium broken

[ZenDay]

Sandcastle example: https://sandcastle.cesium.com/#c=bZCxboMwEIZf5cQSkJCdNBshqBIdK3Vo1cmLgSO1amxkH6S0yrvXQCNVbTbf5/87/bpROhgVntHBEQyeoUSvho69LiwWUb3MpTUklUEnouQgjDC1NZ4Ag7TaDA0pUuiZbJr4SxiA3vpArMmuO0vpKLyk2bPW2e4BTw7Rx9sUtkk6G1pWqDNYbADCD8pgI0S1u9tvVsb5FV/ZJZiXudNPj1ZPLzbG5BClUe5p0lisKsC96nrrCAanY8Y4YddrGRrxaqjfkVjt/bxojub8t5o3agTVHG9cA2otvQ8/7aD1s/pEERU5D/l/qrayUeb0NKLTcppjb7vicYWMsZyH8bZJ1upKuj+bvwE

Browser: Chrome 96.0.4664.55

Operating System: macOS 11.6

Using some special character like '\b' will cause Cesium Broken.

I found that the problem may be at file /Source/Core/writeTextToCanvas.js L46

    var ascent, descent;
    // Find the number of rows (from the top) until the first non-white pixel
    for (i = 0; i < length; ++i) {
      if (pixelData[i] !== 255) {
        ascent = (i / width4) | 0;
        break;
      }
    }

    // Find the number of rows (from the bottom) until the first non-white pixel
    for (i = length - 1; i >= 0; --i) {
      if (pixelData[i] !== 255) {
        descent = (i / width4) | 0;
        break;
      }
    }

    var minx = -1;
    // For each column, for each row, check for first non-white pixel
    for (i = 0; i < width && minx === -1; ++i) {
      for (j = 0; j < height; ++j) {
        var pixelIndex = i * 4 + j * width4;
        if (
          pixelData[pixelIndex] !== 255 ||
          pixelData[pixelIndex + 1] !== 255 ||
          pixelData[pixelIndex + 2] !== 255 ||
          pixelData[pixelIndex + 3] !== 255
        ) {
          minx = i;
          break;
        }
      }
    }

    return {
      width: metrics.width,
      height: descent - ascent,
      ascent: baseline - ascent,
      descent: descent - baseline,
      minx: minx - padding / 2,
    };

We DID NOT initialize ascent and descent as a normal number. When length is equal to 0, the value of ascent and descent would be undefined.
And we will return a object just like:

{
   height: NaN,
   ascent: NaN,
   descent: NaN
}

That would cause Cesium broken.

[ebogo1]

Thanks for reporting this @ZenDay - this looks like a bug and we'll posted updates in this issue once we get a chance to look into it.