【报Bug】3.0.7.20210123 HbuilderX canvas 保存的是空白图片

示例代码：

post() {  
                var that = this  
                uni.showLoading({  
                    title: '保存中'  
                });  
                const context = uni.createCanvasContext('firstCanvas')  

                context.drawImage('http://xxxx.com/xxx.png',0, 0, 375, 473)  //这是背景图片  
                context.drawImage(that.img, 87.5, 150, 200, 200) //这是二维码  

                context.save()  
                context.beginPath()  
                context.arc(44, 350, 25, 0, 2 * Math.PI)  
                context.clip()  
                context.restore()  
                context.draw()  
                setTimeout(function(){  
                    uni.canvasToTempFilePath({  
                        x: 0,  
                        y: 0,  
                        // width: 375,  
                        // height: 473,  
                        // destWidth: 700,  
                        // destHeight: 1000,  
                        canvasId: 'firstCanvas',  
                        success: function(res) {  
                            console.log(res.tempFilePath)  
                            uni.hideLoading()  
                            uni.saveImageToPhotosAlbum({  
                                filePath: res.tempFilePath,  
                                success: function(red) {  
                                    uni.showToast({  
                                        title: '保存相册成功'  
                                    })  
                                },  
                                fail(res) {  
                                    console.log(res)  
                                    if (res.errMsg == "saveImageToPhotosAlbum:fail auth deny") {  
                                        uni.showModal({  
                                            title: '您需要授权相册权限',  
                                            success(res) {  
                                                if (res.confirm) {  
                                                    uni.openSetting({  
                                                        success(res) {  

                                                        },  
                                                        fail(res) {  
                                                            console.log(res)  
                                                        }  
                                                    })  
                                                }  
                                            }  
                                        })  
                                    }  
                                }  
                            });  
                        },  
                        fail(res) {  
                            uni.hideLoading()  
                        }  
                    }, this)  
                },4000)  
            }

操作步骤：

详见上面的示例
const context = uni.createCanvasContext('firstCanvas')

            context.drawImage('http://xxxx.com/xxx.png',0, 0, 375, 473)  
            context.drawImage(that.img, 87.5, 150, 200, 200)  

            context.save()  
            context.beginPath()  
            context.arc(44, 350, 25, 0, 2 * Math.PI)  
            context.clip()  
            context.restore()  
            context.draw()  

uni.canvasToTempFilePath({canvasId: 'firstCanvas',})

预期结果：

用canvasToTempFilePath 保存 canvas绘制的图片，保存到相册，应该正常显示才对

实际结果：

用canvasToTempFilePath 保存 canvas绘制的图片，保存到相册，保存到相册是空白的