pcrlock: ignore empty device path

Don't mark records with empty device path as invalid. When shim is in
use, such records are normal :-/
rhboot/shim#642

src/pcrlock/pcrlock.c

@@ -777,6 +777,16 @@ static int event_log_record_extract_firmware_description(EventLogRecord *rec) {
                 const packed_EFI_DEVICE_PATH *dp = (const packed_EFI_DEVICE_PATH*) load->devicePath;
                 size_t left = load->lengthOfDevicePath;
 
+                /* device path could be empty. Don't mark that as invalid but leave as don't know.
+                 * Happens eg with shim https://github.com/rhboot/shim/issues/642 */
+                if (left == 0) {
+                        rec->description = strdup("File:");
+                        if (!rec->description)
+                                return log_oom();
+
+                        return 1;
+                }
+
                 for (;;) {
                         if (left == 0) {
                                 if (!end) {