[sliceInitialLength] false positive: should allow truncation in append

[seiyab]

Some programmer truncates slice on append.
Following code is reported though this doesn't cause unintended preceding zero values.

https://github.com/ethereum/go-ethereum/blob/3c75c64e6bbf64f842c6f725a595713262c2f8fe/accounts/usbwallet/ledger.go#L501-L507

	chunk := make([]byte, 64)
	space := len(chunk) - len(header)

	for i := 0; len(apdu) > 0; i++ {
		// Construct the new message to stream
		chunk = append(chunk[:0], header...)
		binary.BigEndian.PutUint16(chunk[3:], uint16(i))

[seiyab]

https://github.com/ethereum/go-ethereum/blob/34aac1d7562bf141fe6da1d4f3cdea8819e7b23b/internal/cmdtest/test_cmd.go#L127-L135

func (tt *TestCmd) matchExactOutput(want []byte) error {
	buf := make([]byte, len(want))
	n := 0
	tt.withKillTimeout(func() { n, _ = io.ReadFull(tt.stdout, buf) })
	buf = buf[:n]
	if n < len(want) || !bytes.Equal(buf, want) {
		// Grab any additional buffered output in case of mismatch
		// because it might help with debugging.
		buf = append(buf, make([]byte, tt.stdout.Buffered())...)