Avoid multiple queries to gitlab with no events (#357)

GitLab plugin was accessing GitLab API multiple times if the events set
was empty. Now it accesses the API only once.

Signed-off-by: Sandro Bonazzola <[email protected]>

did/plugins/gitlab.py

@@ -172,7 +172,7 @@ def search(self, user, since, until, target_type, action_name):
         """ Perform GitLab query """
         if not self.user:
             self.user = self.get_user(user)
-        if not self.events:
+        if self.events is None:
             self.events = self.user_events(self.user['id'], since, until)
         result = []
         for event in self.events: