Bug 140395 IImage.getID() return null on chart images
When I use image.getID() to retrieve ID of chart image, it always returns null.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/Image.java
if ( imgUri != null )
				{
						this.id = imgUri;
						this.source = IImage.FILE_IMAGE;
					}
				break;
			case IImageContent.IMAGE_NAME :
				if ( imgData != null )
				{
					this.data = imgData;
					this.source = IImage.DESIGN_IMAGE;
					this.id = imgUri;
				}
				break;
			case IImageContent.IMAGE_EXPRESSION :
				if ( imgData != null )
				{
					this.data = imgData;
					this.source = IImage.CUSTOM_IMAGE;
				}
				break;
			case IImageContent.IMAGE_URI :
				if ( imgUri != null )
				{
					this.id = imgUri;
					this.source = IImage.URL_IMAGE;
				}
				break;
			default :
				assert ( false );