Revert "fix crash on NULL gi.invent"

This reverts commit 378648bd9c.

The problem was triggered by marking the 'objlist' argument in
merge_choice() prototype with __attribute__((nonnull)) when it
shouldn't have been, then a followup which relied on that.  The
'objlist' argument might be Null.  Instead of passing its address to
force it to be non-Null, remove the attribute.

src/files.c

@@ -3885,7 +3885,7 @@ wizkit_addinv(struct obj *obj)
         obj->bknown = 1; /* ok to bypass set_bknown() */
     /* same criteria as lift_object()'s check for available inventory slot */
     if (obj->oclass != COIN_CLASS && inv_cnt(FALSE) >= invlet_basic
-        && !merge_choice(&gi.invent, obj)) {
+        && !merge_choice(gi.invent, obj)) {
         /* inventory overflow; can't just place & stack object since
            hero isn't in position yet, so schedule for arrival later */
         add_to_migration(obj);