[iter] Fix hb_sink() to accept rvalue

src/hb-iter.hh

@@ -569,7 +569,7 @@ HB_FUNCOBJ (hb_apply);
 template <typename Sink>
 struct hb_sink_t
 {
-  hb_sink_t (Sink&& s) : s (s) {}
+  hb_sink_t (Sink s) : s (s) {}
 
   template <typename Iter,
 	    hb_requires (hb_is_iterator (Iter))>

src/test-iter.cc

@@ -185,6 +185,10 @@ main (int argc, char **argv)
   | hb_sink (st)
   ;
 
+  + hb_iter (src)
+  | hb_sink (hb_array (dst))
+  ;
+
   + hb_iter (src)
   | hb_apply (&st)
   ;