Remove 'res is None' test from KeyData.get_uid()

While this could techincally allow reusing already parsed values for
uid, debexpo doesn't call this function twice for the same uid.

debexpo/tools/gnupg.py

@@ -241,8 +241,6 @@ class KeyData():
 
     def get_uid(self, uid):
         uidfpr = uid[7]
-        res = self.uids.get(uidfpr, None)
-        if res is None:
         self.uids[uidfpr] = res = Uid(self, uid)
         return res