ensure_not_tainted_license: skip if not found

This change makes ensure_not_tainted_license.sh only emit a warning if
license file is not found, as opposed to failing.

BUG=chromium:1163996
TEST=N/A
BRANCH=none

Change-Id: I14103bc520efabf3e0c1424e8a5cae259d42c966
Signed-off-by: Sergey Frolov <sfrolov@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2632876
Commit-Queue: George Engelbrecht <engeg@google.com>
Reviewed-by: George Engelbrecht <engeg@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/image_signing/ensure_not_tainted_license.sh b/scripts/image_signing/ensure_not_tainted_license.sh
index cd64049..daa00b5 100755
--- a/scripts/image_signing/ensure_not_tainted_license.sh
+++ b/scripts/image_signing/ensure_not_tainted_license.sh
@@ -42,8 +42,9 @@
 
   license=$(find "${license_dir}" -name about_os_credits.html 2>/dev/null)
   if [[ -z "${license}" ]]; then
-    echo "License file about_os_credits.html not found in ${license_dir}"
-    exit 1
+    echo "License file about_os_credits.html not found in ${license_dir}."
+    echo "Skipping the check of tainted license."
+    exit 0
   fi
 
   tainted_tag="<!-- tainted -->"