ibeta_inv_imp handling cases when (q == 0 or p == 0) or (a == 1 and b == 1)

[agribov_no_s_p_a_m@…]

File: boost\math\special_functions\detail\ibeta_inverse.hpp Function: T ibeta_inv_imp(T a, T b, T p, T q, const Policy& pol, T* py) Line: 480-503. When ((q or p is equal to 0) or (a and b equal to 1)) and invert is true the return value is not reverted. It can be fixed by placing these checks before

if(a == 0.5f) {

std::swap(a, b); std::swap(p, q); invert = !invert;

}

[anonymous]

Confirmed, testing fix.

[John Maddock]

(In [67469]) Fix bug in special-case handling of ibeta_inv. Fix concept test failures with mpfr_class in legendre.hpp and non_central_t.hpp. Fixes #5015.