gerrit: inspect: handle CLs that do not exist

If you try to inspect a CL that doesn't exist (like 1231241251), you get
an ugly traceback.  Print out a proper message instead.

BUG=chromium:327217
TEST=`gerrit inspect 1` shows nice message now instead of traceback

Change-Id: I2f80d27c3355e64f3b0b5b9e006522028625e56d
Reviewed-on: https://chromium-review.googlesource.com/185581
Reviewed-by: Yu-Ju Hong <yjhong@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/gerrit.py b/scripts/gerrit.py
index afc8263..f9cff3c 100644
--- a/scripts/gerrit.py
+++ b/scripts/gerrit.py
@@ -205,7 +205,11 @@
 
 def UserActInspect(opts, idx):
   """Inspect CL number <n>"""
-  PrintCl(opts, FilteredQuery(opts, idx)[0], None)
+  cl = FilteredQuery(opts, idx)
+  if cl:
+    PrintCl(opts, cl[0], None)
+  else:
+    print('no results found for CL %s' % idx)
 
 
 def UserActReview(opts, idx, num):