Readjust mark attachment heuristic a bit more

Previously adjusted logic could fail if nothing around was ligated,
and something moved.  This should take care of that.

CC https://github.com/harfbuzz/harfbuzz/issues/740

src/hb-ot-layout-gpos-table.hh

@@ -1079,7 +1079,10 @@ struct MarkBasePosFormat1
 	  0 == _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) ||
 	  (skippy_iter.idx == 0 ||
 	   _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]) !=
-	   _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx - 1])))
+	   _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx - 1]) ||
+	   _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) !=
+	   _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx - 1]) + 1
+	   ))
 	break;
       skippy_iter.reject ();
     } while (1);