[ucd] Save a few more bytes

Part of https://github.com/harfbuzz/harfbuzz/issues/1652

src/hb-ucd.cc

diff --git a/src/hb-ucd.cc b/src/hb-ucd.cc
index 4d35017..4bdd4f4 100644
--- a/src/hb-ucd.cc
+++ b/src/hb-ucd.cc
@@ -148,19 +148,19 @@
   if (likely (!i)) return false;
   i--;
 
-  if (i < ARRAY_LENGTH (_hb_ucd_dm1_u16_map) + ARRAY_LENGTH (_hb_ucd_dm1_u32_map))
+  if (i < ARRAY_LENGTH (_hb_ucd_dm1_p0_map) + ARRAY_LENGTH (_hb_ucd_dm1_p2_map))
   {
-    if (i < ARRAY_LENGTH (_hb_ucd_dm1_u16_map))
-      *a = _hb_ucd_dm1_u16_map[i];
+    if (i < ARRAY_LENGTH (_hb_ucd_dm1_p0_map))
+      *a = _hb_ucd_dm1_p0_map[i];
     else
     {
-      i -= ARRAY_LENGTH (_hb_ucd_dm1_u16_map);
-      *a = _hb_ucd_dm1_u32_map[i];
+      i -= ARRAY_LENGTH (_hb_ucd_dm1_p0_map);
+      *a = 0x20000 | _hb_ucd_dm1_p2_map[i];
     }
     *b = 0;
     return true;
   }
-  i -= ARRAY_LENGTH (_hb_ucd_dm1_u16_map) + ARRAY_LENGTH (_hb_ucd_dm1_u32_map);
+  i -= ARRAY_LENGTH (_hb_ucd_dm1_p0_map) + ARRAY_LENGTH (_hb_ucd_dm1_p2_map);
 
   uint64_t v = _hb_ucd_dm2_map[i];
   *a = HB_CODEPOINT_DECODE3_1 (v);