Reinit skippy iters when auto_zwj / auto_zwnj change

Ouch.  How did we not hit this bug before...

src/hb-ot-layout-gsubgpos.hh

@@ -508,19 +508,20 @@ struct hb_ot_apply_context_t :
 			random (false),
 			random_state (1) {}
 
-  inline void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; }
-  inline void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; }
-  inline void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; }
-  inline void set_random (bool random_) { random = random_; }
-  inline void set_recurse_func (recurse_func_t func) { recurse_func = func; }
-  inline void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
-  inline void set_lookup_props (unsigned int lookup_props_)
+  inline void reinit_iters (void)
   {
-    lookup_props = lookup_props_;
     iter_input.init (this, false);
     iter_context.init (this, true);
   }
 
+  inline void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; }
+  inline void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; reinit_iters (); }
+  inline void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; reinit_iters (); }
+  inline void set_random (bool random_) { random = random_; }
+  inline void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+  inline void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
+  inline void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; reinit_iters (); }
+
   inline uint32_t random_number (void)
   {
     /* http://www.cplusplus.com/reference/random/minstd_rand/ */