SignaturePad has zero height inside Stepper

[tkennedy13]

When displayed inside a Stepper, the SignaturePad is not useable because the signing canvas is not fully visible. It's like the SignaturePad has a zero height and all that is visible is the buttons.

  ```
                          <MudSignaturePad Elevation="2" 
                                                 Variant="Variant.Outlined"                                                             
                                                 ShowDownload="false"
                                                 ShowLineWidth="false"
                                                 ShowStrokeStyle="false"
                                                 ShowLineCapStyle="false"
                                                 ShowLineJoinStyle="false"                                            
                                                 Options="_options"
                                                 ValueChanged="SignatureChanged"
                                                 Value="SignatureRaw"
                                                 CanvasContainerClass="pa-3" />

    private SignaturePadOptions _options = new SignaturePadOptions
    {
        LineCapStyle = LineCapTypes.Round,
        LineJoinStyle = LineJoinTypes.Round,
        LineWidth = 4,
    };