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: 77f119baf6f4b85194a9b26d8442ddc7fb3bb97c)
(From OE-Core rev: 4cee5c4bc74edde48fe19ec11c78f6c598cf08b6)
Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>