twn_text.c: discard empty inputs

src/rendering/twn_text.c

@@ -253,6 +253,9 @@ void draw_text(const char *string, Vec2 position, int height_px, Color color, co
 
     /* the original string might not be around by the time it's used, so copy it */
     size_t str_length = SDL_strlen(string) + 1;
+    if (str_length == 1)
+        /* empty string */
+        return;
     char *dup_string = string_arena_alloc(&string_arena, str_length);
     SDL_strlcpy(dup_string, string, str_length);