Fix critical bug in JsonValidatorCache

Commit 7f83965011e217ed91008396e016e7f662fba19c introduced a fatal bug: we only
checked for the node size before we decided to return a validator which is
always true.

But all value nodes have size 0! As such, all value nodes would be accounted for
as schemas which would validate every instance successfully.

Not good.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
1.4.6

* Critical bug: all value nodes passed as schemas would be considered as empty
  schemas. Fix.

Francis Galiegue (1):
      Fix critical bug in JsonValidatorCache

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>