sd-device: do no allocate strings of unknown length on the stack
    
    Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=33881.
    
    Not only we would duplicate unknown input on the stack, we would do it
    over and over. So let's first check that the input has reasonable length,
    but also allocate just one fixed size buffer.
    
    (cherry picked from commit e17c95af8e450caacde692875b30675cea75211f)