file.py reset pre_process flag and result on upload

If a sample was edited ad the new file had no pre-process, the status
from the previous pre-process would remain set, and in case of errors,
could sometimes block any runs.

mention #2343

server/web2py/applications/vidjil/controllers/file.py

@@ -504,7 +504,9 @@ def upload():
             error += "no data file"
         if request.vars["file_number"] == "2" and len(error) == 0 and data_file2 is None:
             error += "no data file"
-            
+
+        db.sequence_file[request.vars["id"]] = dict(pre_process_flag=None,
+                                                    pre_process_result=None)
         if data_file is not None and data_file2 is not None and request.vars['pre_process'] != '0':
             db.sequence_file[request.vars["id"]] = dict(pre_process_flag = "WAIT")
             old_task_id = db.sequence_file[request.vars["id"]].pre_process_scheduler_task_id