Currently in NVD DB an item popped up, which hasn't set baseMetricV2.
Let the parser handle it as an optional item.
In case use baseMetricV2 before baseMetricV3
(From OE-Core rev: fdcbf3f28289188c5a97664d1421d4a5c4991eda)
Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>