函数 checkAndConvertImage

checkAndConvertImage(
relativeUrl: string,
callback: (absoluteUrl: string, isAvailable: boolean) => void,
): void
判断是否可用，若图片是相对路径会转换为绝对路径
参数
- relativeUrl: string
  图片地址
- callback: (absoluteUrl: string, isAvailable: boolean) => void
  回调函数
返回 void
示例
```
const relativeUrl: string = 'images/picture.jpg';
checkAndConvertImage(relativeUrl, (absoluteUrl: string, isAvailable: boolean) => {
if (isAvailable) {
     console.log('图片地址可用: ' + absoluteUrl);
 } else {
     console.log('图片地址不可用: ' + absoluteUrl);
   }
});
```
- 定义于 earthsdk/earthsdk3-cesium/src/utils/generalUtils/checkAndConvertImage.ts:15