[kern] Implement format-2 kern subtable

src/hb-ot-kern-table.hh

@@ -116,7 +116,13 @@ struct KernSubTableFormat2
   {
     unsigned int l = (this+leftClassTable).get_class (left);
     unsigned int r = (this+leftClassTable).get_class (left);
-    return 0;//(&(this+array))[0/*XXX*/];
+    unsigned int offset = l * rowWidth + r * sizeof (FWORD);
+    const FWORD *v = &StructAtOffset<FWORD> (&(this+array), offset);
+    /* Untested code, as I have not been able to find ANY kern table format-2 yet. */
+    assert (&(this+array) <= v);
+    if (unlikely (v + 1 > (const FWORD *) end))
+      return 0;
+    return *v;
   }
 
   inline bool sanitize (hb_sanitize_context_t *c) const