Fix error in arrayBuffer when there are extra bytes

[iatll]

Hello, when the number of output bits is large the following occurs:

 h = shake256.create(40);
 h.update("");
 const a = new Uint8Array(h.arrayBuffer());
 a[4]; // 11 as expected

 h = shake256.create(32 * (34 + 1) + 8); 
 h.update("");
 const b = new Uint8Array(h.arrayBuffer());
 a[4]; // 70  but should be 11

[emn178]

Thanks for reporting