restores unintended addition in 43be5ba

restores two lines in restore in _hb_allocate_lig_id function that were unintentionally deleted in 43be5ba

src/hb-ot-layout.hh

@@ -485,6 +485,8 @@ static inline uint8_t
 _hb_allocate_lig_id (hb_buffer_t *buffer)
 {
   uint8_t lig_id = buffer->next_serial () & 0x07;
+  if (unlikely (!lig_id))
+    lig_id = _hb_allocate_lig_id (buffer); /* in case of overflow */
   return lig_id;
 }