Fix race and error case in GN auto-roller script.

tools/gn/bin/roll_gn.py

Index: tools/gn/bin/roll_gn.py
diff --git a/tools/gn/bin/roll_gn.py b/tools/gn/bin/roll_gn.py
index 59a240fd01dae073b7a7e885a2d11c789fe55cc7..6c29b0afbde0eddd85eeca8982a2986a1c5b9d32 100644
--- a/tools/gn/bin/roll_gn.py
+++ b/tools/gn/bin/roll_gn.py
@@ -181,7 +181,8 @@ class GNRoller(object):
   def WaitForBuildToFinish(self):
     print('Checking build')
     results = self.CheckBuild()
-    while any(r['state'] == 'pending' for r in results.values()):
+    while (len(results) or
+           any(r['state'] == 'pending' for r in results.values())):
       print()
       print('Sleeping for 30 seconds')
       time.sleep(30)
@@ -213,7 +214,7 @@ class GNRoller(object):
     try_job_results = patchset_data['try_job_results']
     if not try_job_results:
       print('No try jobs found on most recent patchset')
-      return 1
+      return {}
 
     results = {}
     for job in try_job_results: