Do not get a new connection when retrying to lock table on transaction start

Closes #13661
(grafted from a36a983afe44fc569c04db4d3db71146400b6422)

--HG--
branch : 7.0

trytond/trytond/transaction.py

@@ -192,12 +192,12 @@ class Transaction(object):
             self.counter = 0
             self._datamanagers = []
 
+            self.connection = database.get_connection(readonly=readonly,
+                autocommit=autocommit)
             count = 0
             while True:
                 if count:
                     time.sleep(0.002 * (_retry - count))
-                self.connection = database.get_connection(readonly=readonly,
-                    autocommit=autocommit)
                 try:
                     lock_tables = extras.get('_lock_tables', [])
                     for table in lock_tables: