Infinite loop on pooly defined matrix in UnitQuaternion::from_matrix.

This snippet manages to get the execution stuck when running. I know that the values are bad, but also an infinite loop might not be the most desirable outcome of this.

```rust #[test]
fn infitite_loop() {
let mut rot = na::SMatrix::::zeros();
rot.fill(f64::NAN);
let _q = UnitQuaternion::from_matrix(&rot);
}
```

If the behavior is intended, apologies then.

Start by reproducing the provided test with a NaN-filled 3×3 matrix and tracing UnitQuaternion::from_matrix to identify the loop that fails to terminate. Inspect the invalid-input behavior around that entry point, then add regression coverage showing that non-finite input completes without hanging and matches the project’s expected behavior.

Written by the indexing model from the issue text.