fix memory leaks for #quit while in tutorial

The new change to reset discoveries and monster-stats when exiting
the tutorial used dynamic data which wouldn't be freed if player
used #quit and declined to resume the regular game.

It turns out that such a leak was already present for start-of-game
inventory that gets stashed away during the tutorial.

In both cases, it could happen at most once per game so wasn't a big
deal as far as memory leaks go.

include/decl.h

@@ -422,6 +422,12 @@ struct instance_globals_g {
     /* invent.c */
     long glyph_reset_timestamp;
 
+    /* nhlua.c */
+    boolean gmst_stored;
+    long gmst_moves;
+    struct obj *gmst_invent;
+    genericptr_t *gmst_ubak, *gmst_disco, *gmst_mvitals;
+
     /* pline.c */
     struct gamelog_line *gamelog;