artifacts: Fix error on missing artifact.

BUG=chromium:1094215
TEST=run_pytest

Change-Id: I02c9d678ebf6f7b4d9f69880c2c2683f417d892e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2274910
Commit-Queue: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Auto-Submit: Alex Klein <saklein@chromium.org>
diff --git a/api/controller/artifacts.py b/api/controller/artifacts.py
index ba191b0..de5e58d 100644
--- a/api/controller/artifacts.py
+++ b/api/controller/artifacts.py
@@ -193,7 +193,8 @@
     # Note that this returns the full path to *multiple* tarballs.
     archives = artifacts.BundleAutotestFiles(chroot, sysroot, output_dir)
   except artifacts.Error as e:
-    cros_build_lib.Die(e)
+    logging.warning(e)
+    return
 
   for archive in archives.values():
     output_proto.artifacts.add().path = archive