padding: channel of image is 3 but length of fill is 1

[Domibor]

Problem:
Padding does not work when fill is a scalar, but the image is RGB.

What happens:
Using a scalar for fill in combination with an RGB image crashes.
cvfunctional.pad() assumes a fill of length 3 for an RGB image, but the default value of cvtransforms.Pad() is 0 (length 1).

What should happen:
If fill is a scaler, it should be used for all 3 channels.

[hityzy1122]

Problem:
Padding does not work when fill is a scalar, but the image is RGB.

What happens:
Using a scalar for fill in combination with an RGB image crashes.
cvfunctional.pad() assumes a fill of length 3 for an RGB image, but the default value of cvtransforms.Pad() is 0 (length 1).

What should happen:
If fill is a scaler, it should be used for all 3 channels.

I think I have fixed some bugs as your suggestion. Thanks a lot!

[buptlj]

here is a bug:
`

if isinstance(fill, numbers.Number):
fill = fill,
if isinstance(fill, numbers.Number) and len(img.shape) == 3:
fill = (fill,) * 3

`
the type of fill is changed in line 2.

第二行改变了fill的类型，变成tuple了，即使img.shape是3，第四行也不会执行了。

[hityzy1122]

here is a bug:
`

if isinstance(fill, numbers.Number):
fill = fill,
if isinstance(fill, numbers.Number) and len(img.shape) == 3:
fill = (fill,) * 3

`
the type of fill is changed in line 2.

第二行改变了fill的类型，变成tuple了，即使img.shape是3，第四行也不会执行了。

Thanks !
I hope I have fixed this bug properly ^^.
谢谢，我希望我已经修改好了这个问题^^