[FIX] base: Make sure start time is not undefined

As debugging might be enabled during runtime we need to make sure that
the condition does only pass in case start time is defined

odoo/addons/base/ir/ir_cron.py

@@ -114,10 +114,11 @@ class ir_cron(models.Model):
                 if hasattr(model, method_name):
                     log_depth = (None if _logger.isEnabledFor(logging.DEBUG) else 1)
                     odoo.netsvc.log(_logger, logging.DEBUG, 'cron.object.execute', (self._cr.dbname, self._uid, '*', model_name, method_name)+tuple(args), depth=log_depth)
+                    start_time = False
                     if _logger.isEnabledFor(logging.DEBUG):
                         start_time = time.time()
                     getattr(model, method_name)(*args)
-                    if _logger.isEnabledFor(logging.DEBUG):
+                    if start_time and _logger.isEnabledFor(logging.DEBUG):
                         end_time = time.time()
                         _logger.debug('%.3fs (%s, %s)', end_time - start_time, model_name, method_name)
                     self.pool.signal_caches_change()