solve_deg3 gives incorrect result (polynom_solver.cpp)

function **solve_deg3** from `opencv/modules/calib3d/src/polynom_solver.cpp`
gives an incorrect result = -nan 
for a=3.0, b=3.0, c=1.0, d=1.0

```c++
double x0, x1, x2;

auto n = solve_deg3(3.0, 3.0, 1.0, 1.0, x0, x1, x2);
```

n is 1
x0 is -nan(ind) but it should be -1.0

Compiled and run in MS VisualStudio 2019.