scripts: fix process metric

There can be some defunct process which breaks the original code.

BUG=None
TEST=None

Change-Id: Ie650287526e085dcba52f457cfa375c7a8049005
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4201448
Tested-by: Congbin Guo <guocb@chromium.org>
Auto-Submit: Congbin Guo <guocb@chromium.org>
Commit-Queue: Congbin Guo <guocb@chromium.org>
Reviewed-by: Sergey Fetisov <sfetisov@google.com>
diff --git a/scripts/sysmon/proc_metrics.py b/scripts/sysmon/proc_metrics.py
index 01b0e67..6f5e0c5 100644
--- a/scripts/sysmon/proc_metrics.py
+++ b/scripts/sysmon/proc_metrics.py
@@ -220,4 +220,4 @@
     'podman run --option ... image:tag'
     """
     cmdline = proc.cmdline()
-    return proc.name() == "podman" and cmdline[1] == subcmd
+    return proc.name() == "podman" and len(cmdline) > 1 and cmdline[1] == subcmd