Fix sqrt(0) panic in managed math

[Rexicon226]

fixes #17858

when the a value takes 0 bits, it will always be 0, by extension the square root will always be 0.

i also added a negative check that returns an error. because the current error is very misleading:

/home/dr/zig/lib/std/debug.zig:342:14: 0x222c22 in assert (test)
    if (!ok) unreachable; // assertion failure
             ^
/home/dr/zig/lib/std/math/big/int.zig:1524:15: 0x2293ef in div (test)
        assert(!y.eqlZero()); // division by zero