Base64 String Image in background is distorted
**Describe the bug**
When we provide a base64 encoded string of an image to the prop backgroundImage, the background image is not showing up properly, it is distorted and with very small height(not filling the canvas and not recognizable)

**To Reproduce**
```
                            <ReactSketchCanvas
                                ref={ canvasRef }
                                style={{
                                    border: '0.0625rem solid #9c9c9c',
                                    borderRadius: '0.25rem'
                                }}
                                height={ naturalHeight }
                                width={ naturalWidth }
                                strokeWidth={ 4 }
                                strokeColor="red"
                                backgroundImage={ base64String }
                                exportWithBackgroundImage
                            />
```

**Expected behavior**
The background image should be displayed in the canvas with the height and width of the actual image

**Desktop (please complete the following information):**
 - OS: iOS
 - Browser : Chrome
 - Version : 96.0.4664.110 (Official Build) (x86_64)


**Additional context**
When the sketched image is downloaded, it is getting downloaded correctly.
