Request the hardware context when a game loads

retro_init() read the core options, and with them asked for the
hardware context. libretro.h says to set it in retro_load_game(), and
a frontend that only accepts it then (Kodi) turned it down, so the
core fell back to software and never asked again.

libretro.c

@@ -641,8 +641,6 @@ void retro_init(void)
 
    environ_cb(RETRO_ENVIRONMENT_SET_PERFORMANCE_LEVEL, &level);
 
-   check_variables();
-
    vecx_psg_set_buffer(psgbuf);
    vecx_dac_set_buffer(dacbuf);
 }
@@ -695,6 +693,9 @@ bool retro_load_game(const struct retro_game_info *info)
 
    if (!info)
       return false;
+
+   /* Frontends may only accept a hardware context once a game is loading */
+   check_variables();
 #ifdef HAS_GPU
    if (usingHWContext)
       usingHWContext = set_rendering_context(true);