Math.sqrt reverts given uint(-1)

[MrChico]

The current implementation of sqrt, copied here for convenience:

1.     function sqrt(uint y) internal pure returns (uint z) {
2.         if (y > 3) {
3.             uint x = (y + 1) / 2;
4.             z = y;
5.             while (x < z) {
6.                 z = x;
7.                 x = (y / x + x) / 2;
8.             }
9.         } else if (y != 0) {
10.            z = 1;
11.        }
12.    }

reverts given the argument uint(-1), as this sets x to zero, leading to a division by zero error at line 7.

An easy fix is to change L3 to uint x = y / 2 + 1;, which makes the function well defined for uint(-1) as well.