added DataStore.clearCurrentTask()

DataStore.py

@@ -73,15 +73,21 @@ WHERE id = 0
         return ct
 
     def updateCurrentTask(self, ct):
+        self.clearCurrentTask()
+        c = self.conn.cursor()
+        c.execute('''
+INSERT INTO history
+VALUES (0, ?, ?)
+''', (ct.taskid, ct.dt.strftime(HISTORY_DT_FMT)))
+        c.close()
+        self.conn.commit()
+
+    def clearCurrentTask(self, ct):
         c = self.conn.cursor()
         c.execute('''
 DELETE FROM history
 WHERE id = 0
 ''')
-        c.execute('''
-INSERT INTO history
-VALUES (0, ?, ?)
-''', (ct.taskid, ct.dt.strftime(HISTORY_DT_FMT)))
         c.close()
         self.conn.commit()