Fix caught signals check

[w0nsh]

Hi.
The caughtSignals mask should be shifted by one, since the first bit corresponds to the signal with number 1.

[Michcioperz]

I think I need another pair of eyes on this, but it does seem to make sense

[Wolf480pl]

Yup, tested and indeed the lowest bit of SigCgt mask corresponds to signal 1, not 0, at least on kernels 5.15 and 3.13.
The fix is correct, but it I think it needs a comment in the code explaining why we shift.

[Wolf480pl]

The fix is correct but requires a comment in the code explaining why the shift. ( misclicked accept, sorry)