[infra] profile command: do not fail hard if some fuzz targets have no corpus. (#1719)

* [infra] profile command: do not fail hard if some fuzz targets have no corpus.

* Change listing to corpus_listing to be more explicit.

* Address review comment from Abhishek

infra/helper.py

@@ -534,9 +534,19 @@ def _get_latest_corpus(project_name, fuzz_target, base_corpus_dir):
       'ls',
       corpus_backup_url
   ]
-  output = subprocess.check_output(command).splitlines()
+
+  corpus_listing = subprocess.Popen(
+      command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+  output, error = corpus_listing.communicate()
+
+  # Some fuzz targets (e.g. new ones) may not have corpus yet, just skip those.
+  if corpus_listing.returncode:
+    print('WARNING: corpus for {0} not found:\n{1}'.format(fuzz_target, error),
+          file=sys.stderr)
+    return
+
   if output:
-    latest_backup_url = output[-1]
+    latest_backup_url = output.splitlines()[-1]
     archive_path = corpus_dir + '.zip'
     command = [
         'gsutil',