The plot of RP limit state function is incomplete

[mbaudin47]

In the following example:

https://github.com/mbaudin47/otbenchmark/blob/master/examples/reliability_problems/RP25_Demo.ipynb

The plot shows only one single faulty domain:

But the function has two limit state sub-domains. The problem is that the range of X1, X2 must be extended so that the interval is larger.