ci: no-exit: Skip check if no files to check

If we find no files to check, gracefully quit the test.
Formerly, if the list was empty we ended up trying to read
from stdin, and thus hung.

Signed-off-by: Graham Whaley <graham.whaley@intel.com>

.ci/go-no-os-exit.sh

@@ -22,6 +22,8 @@ for f in $candidates; do
 	files="$f $files"
 done
 
+[ -z "$files" ] && echo "No files to check, skipping" && exit 0
+
 if egrep -n '\<os\.Exit\>' $files; then
 	echo "Direct calls to os.Exit() are forbidden, please use exit() so atexit() works"
 	exit 1