fix bugs on reload of logbook

parsers/logbooks.py

@@ -543,6 +543,9 @@ def clean_logbook_for_expedition(expedition):
     """Only used when loading a single logbook. Deletes database LogBookEntries and  
     DataIssues for this expedition year.
     """
+    global tripsdate
+    tripsdate = {}
+    
     lbes = LogbookEntry.objects.filter(expedition=expedition).delete() 
     dataissues = DataIssue.objects.filter(parser="logbooks")
     for di in dataissues: