[Findit] Fix a bug that MonitorTryJobPipeline still runs when no try job scheduled.

appengine/findit/waterfall/identify_try_job_culprit_pipeline.py

Index: appengine/findit/waterfall/identify_try_job_culprit_pipeline.py
diff --git a/appengine/findit/waterfall/identify_try_job_culprit_pipeline.py b/appengine/findit/waterfall/identify_try_job_culprit_pipeline.py
index e59c99796299dd9c27f06438fab9edfa1bc48c54..12be524fe7fe94d697e053b80b743b824dd5c3b3 100644
--- a/appengine/findit/waterfall/identify_try_job_culprit_pipeline.py
+++ b/appengine/findit/waterfall/identify_try_job_culprit_pipeline.py
@@ -278,7 +278,7 @@ class IdentifyTryJobCulpritPipeline(BasePipeline):
     Please refer to try_job_result_format.md for format check.
     """
     culprits = None
-    if result and result.get('report'):
+    if try_job_id and result and result.get('report'):
       try_job_data = WfTryJobData.Get(try_job_id)
       if try_job_type == failure_type.COMPILE:
         # For compile failures, the try job will stop if one revision fails, so
@@ -340,4 +340,4 @@ class IdentifyTryJobCulpritPipeline(BasePipeline):
     UpdateWfAnalysisWithTryJobResult()
 
     _NotifyCulprits(master_name, builder_name, build_number, culprits)
-    return result.get('culprit') if result else None
+    return result.get('culprit') if result else None