bus-message: do not crash on message with a string of zero length
    
    We'd calculate the "real" length of the string as 'item_size - 1', which does
    not work out well when item_size == 0.
    
    (cherry picked from commit 81b6e63029eefcb0ec03a3a7c248490e38106073)
    
    Resolves: #1635439
    
    patch_name: 0025-bus-message-do-not-crash-on-message-with-a-string-of.patch
    present_in_specfile: true
    location_in_specfile: 25
    squash_commits: true