fs/hfsplus: Set a grub_errno if mount fails

It was possible for mount to fail but not set grub_errno. This led to
a possible double decrement of the module reference count if the NULL
page was mapped.

Fixing in general as a similar bug was fixed in commit 61b13c187
(fs/hfsplus: Set grub_errno to prevent NULL pointer access) and there
are likely more variants around.

Fixes: CVE-2024-45783

Reported-by: B Horn <b@horn.uk>
Signed-off-by: B Horn <b@horn.uk>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/fs/hfsplus.c

@@ -405,7 +405,7 @@ grub_hfsplus_mount (grub_disk_t disk)
 
  fail:
 
-  if (grub_errno == GRUB_ERR_OUT_OF_RANGE)
+  if (grub_errno == GRUB_ERR_OUT_OF_RANGE || grub_errno == GRUB_ERR_NONE)
     grub_error (GRUB_ERR_BAD_FS, "not a HFS+ filesystem");
 
   grub_free (data);