Only prefer AAT morx for horizontal layout

Fixes #2124.

src/hb-ot-shape.cc

diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 8743387..1769501 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -70,7 +70,8 @@
 						map (face, props),
 						aat_map (face, props)
 #ifndef HB_NO_AAT_SHAPE
-						, apply_morx (hb_aat_layout_has_substitution (face))
+                        /* https://github.com/harfbuzz/harfbuzz/issues/2124 */
+						, apply_morx (HB_DIRECTION_IS_HORIZONTAL(props->direction) && hb_aat_layout_has_substitution (face))
 #endif
 {
   shaper = hb_ot_shape_complex_categorize (this);