Description

In some rare cases ShiftLeft panics in bitset.go#1490. Minimal example:

a := New(0)
a.Set(560)
a.ShiftLeft(16) // panic

Fix

I believe this is just "off by one" error in the calculation of the needed size. I didn't dig much deeper, so it's possible that this bug has a better fix.

A value that caused panic is added into TestShiftLeft, hovewer this case could be minified if needed.