panic slice bounds out of range,why?

panic: runtime error: slice bounds out of range [96:48]

goroutine 12291275 [running]:
bufio.(*Reader).ReadSlice(0xc01c8e4d80, 0x4cd50a, 0xc0004d9080, 0xc01220c000, 0x6, 0x1000, 0x6)
C:/Go/src/bufio/bufio.go:334 +0x230
bufio.(*Reader).ReadBytes(0xc01c8e4d80, 0x45020a, 0xc024f8cea8, 0xc008e995d0, 0x5e39ae, 0xc0004d9080, 0xc01220c000)
C:/Go/src/bufio/bufio.go:438 +0x7a
bufio.(*Reader).ReadString(...)
C:/Go/src/bufio/bufio.go:475
github.com/dutchcoders/goftp.(*FTP).receiveLine(0xc022fbdd80, 0x4fdca5, 0xc0000ca860, 0xc01220c000, 0x6)
C:/Users/win7/go/pkg/mod/github.com/dutchcoders/goftp@v0.0.0-20170301105846-ed59a591ce14/ftp.go:281 +0x38
github.com/dutchcoders/goftp.(*FTP).receive(0xc022fbdd80, 0xd629cf, 0x4, 0x0, 0x0)
C:/Users/win7/go/pkg/mod/github.com/dutchcoders/goftp@v0.0.0-20170301105846-ed59a591ce14/ftp.go:291 +0x40
github.com/dutchcoders/goftp.(*FTP).cmd(0xc022fbdd80, 0xd6225f, 0x3, 0xd629cf, 0x4, 0x0, 0x0, 0x0, 0x47e2ac, 0xc0006f1890, ...)
C:/Users/win7/go/pkg/mod/github.com/dutchcoders/goftp@v0.0.0-20170301105846-ed59a591ce14/ftp.go:149 +0x91
github.com/dutchcoders/goftp.(*FTP).Pasv.func1(0xc00079b260, 0xc022fbdd80, 0xc0081c98d0, 0xc024f8ce98)
C:/Users/win7/go/pkg/mod/github.com/dutchcoders/goftp@v0.0.0-20170301105846-ed59a591ce14/ftp.go:384 +0xaf
created by github.com/dutchcoders/goftp.(*FTP).Pasv
C:/Users/win7/go/pkg/mod/github.com/dutchcoders/goftp@v0.0.0-20170301105846-ed59a591ce14/ftp.go:379 +0xbf