cryptsetup: don't assert on variable which is optional
    
    https://github.com/systemd/systemd/commit/50d2eba27b9bfc77ef6b40e5721713846815418b#commitcomment-34519739
    
    In add_crypttab_devices() split_keyspec is called on the keyfile argument,
    which may be NULL.
    
    (cherry picked from commit fef716b28be6e866b8afe995805d5ebe2af6bbfa)
    
    Related: #1763155
    
    patch_name: 0300-cryptsetup-don-t-assert-on-variable-which-is-optiona.patch
    present_in_specfile: true
    location_in_specfile: 300
    squash_commits: true