Do not fail if ISO doesn't have grub.cfg inside efi.img

If an ISO doesn't support Secure Boot then the grub.cfg file doesn't
exist inside the efi.img, so we shouldn't continue with its execution.
Use search_file() instead which is unset if the file doesn't exist and
therefore execution gets skipped.

Follow up fix for commit 92ffc08bb28f73c

diff --git a/grml2usb b/grml2usb
index 0199fd6..d206f1d 100755 (executable)
--- a/grml2usb
+++ b/grml2usb
@@ -1760,7 +1760,7 @@ def handle_secure_boot(target, efi_img):
         logging.critical("Fatal: %s", error)
         sys.exit(1)
 
-    grub_cfg = efi_mountpoint + "/boot/grub/grub.cfg"
+    grub_cfg = search_file("grub.cfg", efi_mountpoint + "/boot/grub/")
     logging.debug("grub_cfg = %s" % grub_cfg)
     if not grub_cfg:
         logging.info(