"runtime error: index out of range" while imploding large data

[Grille]

Hi
When trying to compress an large amount of data I get an error.
In my case with settings (Binary, DictionarySize1024) I get an error at around 12kb, with 2048 and 4096 even at less.

exploding works fine

panic: runtime error: index out of range [18446744073709551615] with length 8708

goroutine 1 [running]:
main.getBytePairHash(...)
        writer.go:175
main.sortBuffer(0xc0000ea000, 0x0, 0x2001)
        writer.go:218 +0x1a8
main.writeCmpData(0xc0000ea000)
        writer.go:613 +0x187
main.implode({0x23d6e0, 0xc0000c2480}, {0x23d700, 0xc0000c2450}, 0xc0000ea000, 0x1fa52590dd8, 0x11)
        writer.go:811 +0x22a
main.(*Writer).Close(...)
        writer.go:853