Do not allocate a separate buffer for the transfer.
```
name old time/op new time/op delta
NEP17TransferLog_Append-8 58.8µs ± 3% 32.1µs ± 1% -45.40% (p=0.000 n=10+9)
name old alloc/op new alloc/op delta
NEP17TransferLog_Append-8 118kB ± 1% 44kB ± 3% -63.00% (p=0.000 n=9+10)
name old allocs/op new allocs/op delta
NEP17TransferLog_Append-8 901 ± 1% 513 ± 3% -43.08% (p=0.000 n=9+8)
```
Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>
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