Fix off-by-one in quote-stripping routines

Reported by Oracle Parfait:

Error: Buffer overrun
   Buffer overflow [buffer-overflow] (CWE 120):
      In pointer dereference of key[(len - 1)] with index (len - 1)
      Array size >= 1 bytes, index >= 1
        at line 1647 of process.c in function 'do_add'.

Error: Buffer overrun
   Buffer overflow [buffer-overflow] (CWE 120):
      In pointer dereference of authdata[(authdatalen - 1)] with index (authdatalen - 1)
      Array size is ??? bytes, index is ???
        at line 1965 of process.c in function 'do_generate'.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
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