MAINT: special.hankel2: fix edge case (#21577)

* MAINT: special.hankel2: fix edge case

* Apply suggestions from code review

Co-authored-by: Albert Steppi <[email protected]>

* Update scipy/special/tests/test_basic.py

---------

Co-authored-by: Albert Steppi <[email protected]>

Author: mdhaber

scipy/special/xsf/bessel.h

@@ -1172,6 +1172,11 @@ inline std::complex<double> cyl_hankel_2(double v, std::complex<double> z) {
     if (isnan(v) || isnan(z.real()) || isnan(z.imag())) {
         return cy;
     }
+    if (v == 0 && z == 0.0) {
+        cy.real(NAN);
+        cy.imag(INFINITY);
+        return cy;
+    }
     if (v < 0) {
         v = -v;
         sign = -1;