Prevent resource leak in SDL backend

When twin_sdl_init() fails after successful SDL_Init() but before
completion (e.g., SDL_CreateWindow fails), the SDL subsystem is not
properly cleaned up, leaking system resources.

The bail chain was missing SDL_Quit() cleanup. Error paths jumped
directly to 'bail' label which only freed memory, leaving SDL
initialized.

Author: jserv

backend/sdl.c

@@ -137,7 +137,7 @@ twin_context_t *twin_sdl_init(int width, int height)
                                SDL_WINDOW_SHOWN);
     if (!tx->win) {
         log_error("%s", SDL_GetError());
-        goto bail;
+        goto bail_sdl;
     }
 
     tx->pixels = malloc(width * height * sizeof(*tx->pixels));
@@ -192,6 +192,8 @@ twin_context_t *twin_sdl_init(int width, int height)
     free(tx->pixels);
 bail_window:
     SDL_DestroyWindow(tx->win);
+bail_sdl:
+    SDL_Quit();
 bail:
     free(ctx->priv);
     free(ctx);