Merge pull request #3454 from xinye-hpe/bugfix/failure-stat

[bugfix] Treat correctly `failed_stage=None` in failure stats report

Author: vkarak

reframe/frontend/printer.py

@@ -195,6 +195,9 @@ def failure_stats(self, report, global_stats=False):
                 info += f' @{tc["system"]}:{tc["partition"]}+{tc["environ"]}'
 
                 failed_stage = tc['fail_phase']
+                if not failed_stage:
+                    continue
+
                 failures.setdefault(failed_stage, [])
                 failures[failed_stage].append(info)