Add _MAX_VALUE to hb_ot_metrics_t (#1861)

src/hb-ot-metrics.cc

@@ -53,7 +53,7 @@ _hb_ot_metrics_get_position_common (hb_font_t       *font,
 				    hb_position_t   *position     /* OUT.  May be NULL. */)
 {
   hb_face_t *face = font->face;
-  switch ((unsigned int) metrics_tag)
+  switch ((unsigned) metrics_tag)
   {
 #ifndef HB_NO_VAR
 #define GET_VAR face->table.MVAR->get_var (metrics_tag, font->coords, font->num_coords)
@@ -117,7 +117,7 @@ hb_ot_metrics_get_position (hb_font_t       *font,
 			    hb_position_t   *position     /* OUT.  May be NULL. */)
 {
   hb_face_t *face = font->face;
-  switch (metrics_tag)
+  switch ((unsigned) metrics_tag)
   {
   case HB_OT_METRICS_HORIZONTAL_ASCENDER:
   case HB_OT_METRICS_HORIZONTAL_DESCENDER:

src/hb-ot-metrics.h

@@ -70,7 +70,9 @@ typedef enum {
   HB_OT_METRICS_STRIKEOUT_SIZE			= HB_TAG ('s','t','r','s'),
   HB_OT_METRICS_STRIKEOUT_OFFSET		= HB_TAG ('s','t','r','o'),
   HB_OT_METRICS_UNDERLINE_SIZE			= HB_TAG ('u','n','d','s'),
-  HB_OT_METRICS_UNDERLINE_OFFSET		= HB_TAG ('u','n','d','o')
+  HB_OT_METRICS_UNDERLINE_OFFSET		= HB_TAG ('u','n','d','o'),
+
+  _HB_OT_METRICS_MAX_VALUE = HB_TAG_MAX_SIGNED /*< skip >*/
 } hb_ot_metrics_t;
 
 HB_EXTERN hb_bool_t