[subset] Make ClassDef format2 .intersects() return false if range value 0

We treat Class0 as "doesn't intersect".  That's the only meaningful
interpretation. If one allos Class0 to mean "intersects", then the
intersects() result should be true iff glyphset is non-empty.

Related to https://github.com/harfbuzz/harfbuzz/issues/2703

src/hb-ot-layout-common.hh

@@ -1969,8 +1969,11 @@ struct ClassDefFormat2
     /* TODO Speed up, using hb_set_next() and bsearch()? */
     unsigned int count = rangeRecord.len;
     for (unsigned int i = 0; i < count; i++)
-      if (rangeRecord[i].intersects (glyphs))
+    {
+      const auto& range = rangeRecord[i];
+      if (range.intersects (glyphs) && range.value)
 	return true;
+    }
     return false;
   }
   bool intersects_class (const hb_set_t *glyphs, uint16_t klass) const