lib/dom: avoid crash on empty tags data access
lib/dom: avoid crash on empty tags data access

Signed-off-by: Alexandre Terrasa <b30f4169e054ee7b8c243480bcfcef62416f3b08@moz-code.org>

privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit