增加image-utils工具拼接图片时对图片不存在的兼容

stmms-web/src/main/webapp/static/utils/image-utils.js

@@ -216,7 +216,7 @@ ImageLoader.prototype.combine = function (urls, canvas, config, onSuccess, onErr
         let height = 0
         for (let i = 0; i < config.length; i++) {
             let image = images[config[i].i - 1]
-            if (image.loaded === true) {
+            if (image && image.loaded === true) {
                 context.drawImage(image, config[i].x, config[i].y, config[i].w, config[i].h, 0, height, config[i].w * ratio, config[i].h * ratio)
                 layout.push({
                     ratio: ratio,