Blur fix

[yunline]

fix #2102

[oddbookworm]

LGTM! Fixes the linked issue nicely

[yunline]

Solved another problem when use gaussian_blur in place.
I think it can be a part of this PR.

import pygame
import sys

sf=pygame.image.load("peppers3.tif")
pygame.display.init()
dsf=pygame.display.set_mode((1280,720))
ddsf=dsf.subsurface((720,100,200,300))

while 1:
    dsf.fill((0,150,0))

    dsf.blit(sf, (640,0,0,0))

    pygame.transform.gaussian_blur(ddsf,50,dest_surface=ddsf)

    #dsf.blit(sf,(0,0,1,1))
    pygame.display.update()
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            sys.exit()

Before fix

After fix

[yunline]

It might be better to raise an error instead of creating a buffer when handling in-place operation.
People might think in-place operation is faster, but it's actually slower.

[Starbuck5]

It might be better to raise an error instead of creating a buffer when handling in-place operation.
People might think in-place operation is faster, but it's actually slower.

So an error if the source and destination surfaces are the same? I'm totally okay with that.

[yunline]

So an error if the source and destination surfaces are the same? I'm totally okay with that.

OK, I'll open another PR for this