rendering.c: only update opengl viewport once it's actually changed

src/input.h

@@ -54,7 +54,6 @@ struct action_hash_item {
 
 struct input_state {
     struct action_hash_item *action_hash;
-    SDL_Renderer *renderer; /* some input relates to the screen in some way */
     const uint8_t *keyboard_state; /* array of booleans indexed by scancode */
     uint32_t mouse_state;          /* SDL mouse button bitmask */
     t_vec2 mouse_window_position;