proposed fix: set curr_src.h to bottom_height before drawing bottom edges / corners in SDL_RenderTexture9Grid

[l-t-m-f]

(...in order to avoid issue where inadvertently using top height, if the npatch existed on a larger texture than the drawn edge, would cause too many pixels to be included in the bottom part of the render.)

Description

There is a bug currently with SDL_RenderTexture9Grid, its hard to notice.

Two (2) conditions are needed to trigger, that I noticed.

a) The 9Grid texture is larger in height than the full size of the 9Grid, for example, if there is empty space bellow due to the 9Grid being stored on a spritesheet (streaming texture in minimal reproduce provided).

b) The 9Grid texture has different top and bottom margins.

Then when drawing the 9Grid, top_height was inadvertently used as curr_src.h when drawing lower_left and lower_right, as well as bottom of the 9Grid, causing either extra pixels to be drawn (resulting in squished bottom part of the 9Grid) or cropped (haven't tested that second case). curr_src.h should have been set to bottom_height before these operations. If the 9Grid is stored on a perfectly sized texture, and top_height> bottom_height, then even if the issue was technically occuring, it wasn't having any visual impact due to the texture naturally "ending" when problem should arise...

Anyway, hope I make myself clear. The fix is pretty simple.

This is a minimal example which demonstrates the problem:
https://pastecode.io/s/pi5qo9o1

I used a 50x50 image with margins L=10, R=10, T=14, B=10, placed on a larger 100x100 sheet, which demonstrates the problem.
Image if you want to test it :

[slouken]

Merged, thanks!

[slouken]

@Oen44, do you need this fix in #12076?

[Oen44]

@Oen44, do you need this fix in #12076?

Yeah, I will add this there as well, it just makes sense.