SDL3 multiviewport fix for non-shared textures (for fonts only)

[HDAKFD]

Very nasty fix for SDL3 not being able to share fonts between renderers, but it works.

Though i think this needs better solution, pointer comparing isn't the best approach

SDL_Texture * tex = (SDL_Texture*)pcmd->GetTexID();

if (tex == bd->FontTexture)
{
    if (texture != nullptr)
    {
        tex = texture;
    }
}

[ocornut]

This is probably reliant on certain backend and os and is unlikely to work with all of them supported by SDL.

[HDAKFD]

This is probably reliant on certain backend and os and is unlikely to work with all of them supported by SDL.

It might be, also after doing some research i found out that there is ways to copy the textures between renderers rather than recreating them.

Though SDL3 still to this date does not support sharing textures between 2 different SDL_Renderer instances without any extra code. So something needs to be done about it.

[ocornut]

It’s well known what needs to be done, but SDL Renderer for some backends creates one device per renderer making the textures non sharable.
See my link #7675 (comment)
I can tell your PR isn’t going to work accross multiple renderers.