Ticket 49493 - heap use after free in csn_as_string
    
    Bug: If write_changlog_and_ruv failed teh csn pending list was not properly
         cleand and references to the prim csn were kept, but the prim csn was reset
    
    Fix: check the return code for the mmr postop plugin and aset error codes properly
         that will triger cancel_opcsn
    
    Reviewed by: Thierry, thanks
    Tested by: Viktor, thanks