Certain unit quaternions produce invalid rotation matrices

Case in point, take this quaternion:

```rust
let q = UnitQuaternion::new_normalize(Quaternion::new(
0.1045170328727042,
-0.6993398242910853,
0.10451703287270421,
0.6993398242910854,
));
```
then convert it to rotation matrix:
```rust
dbg!(q.to_rotation_matrix());
```

You'll likely get:

```
[
[
-1.6653345369377348e-16,
0.0,
-1.0000000000000002,
],
[
-0.2923716936184902,
-0.9563047593579446,
2.7755575615628914e-17,
],
[
-0.9563047593579445,
0.29237169361849025,
1.6653345369377348e-16,
],
]
```

Notice that the last component of the first row is less than -1. This will create issues (of the NAN variety) if, say, this matrix is then converted to Euler angles.