cve-update: handle baseMetricV2 as optional

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)

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/meta/cve-update-db-native.bb

@@ -160,15 +160,20 @@ def update_db(c, jsondata):
         if not elt['impact']:
             continue
 
+        accessVector = None
         cveId = elt['cve']['CVE_data_meta']['ID']
         cveDesc = elt['cve']['description']['description_data'][0]['value']
         date = elt['lastModifiedDate']
-        accessVector = elt['impact']['baseMetricV2']['cvssV2']['accessVector']
-        cvssv2 = elt['impact']['baseMetricV2']['cvssV2']['baseScore']
-
         try:
+            accessVector = elt['impact']['baseMetricV2']['cvssV2']['accessVector']
+            cvssv2 = elt['impact']['baseMetricV2']['cvssV2']['baseScore']
+        except KeyError:
+            cvssv2 = 0.0
+        try:
+            accessVector = accessVector or elt['impact']['baseMetricV3']['cvssV3']['attackVector']
             cvssv3 = elt['impact']['baseMetricV3']['cvssV3']['baseScore']
-        except:
+        except KeyError:
+            accessVector = accessVector or "UNKNOWN"
             cvssv3 = 0.0
 
         c.execute("insert or replace into NVD values (?, ?, ?, ?, ?, ?)",