Process on a copy of imported data

The process_lines of ModelStorage.import_data pop rows when importing One2Many.
But if the transaction has to be restarted for example if a lock is needed, the
original data from the request has been altered for the second call losing some
or all the data to be imported.

Closes #13984
(grafted from 2cb96c1427d7c0edcb1c9b5b410e220db3f8958e)

--HG--
branch : 7.0

trytond/trytond/model/modelstorage.py

@@ -1113,7 +1113,8 @@ class ModelStorage(Model):
         to_create, to_create_translations = [], []
         to_write, to_write_translations = [], []
         languages = set()
-        while len(data):
+        data = data.copy()
+        while data:
             (row, _, translate) = \
                 process_lines(data, [], fields_def)
             if dispatch(to_create, to_write, row):