Always allocate new ligature id

No practical point in reusing ligature ids.

src/hb-ot-layout-gsub-private.hh

@@ -393,13 +393,10 @@ struct Ligature
 					     : HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE);
 
     if (j == c->buffer->i + i) /* No input glyphs skipped */
-      /* We don't use a new ligature ID if there are no skipped
-	 glyphs and the ligature already has an ID. */
       c->buffer->add_output_glyphs_be16 (i,
 					 1, (const uint16_t *) &ligGlyph,
 					 0,
-					 c->buffer->info[c->buffer->i].lig_id() && !c->buffer->info[c->buffer->i].component() ?
+					 c->buffer->allocate_lig_id ());
-					 0xFFFF : c->buffer->allocate_lig_id ());
     else
     {
       unsigned int lig_id = c->buffer->allocate_lig_id ();