fix find_psi_2nd_separatrix for double nulls

mention @ggdose

Author: orso82

src/physics/fluxsurfaces.jl

@@ -732,9 +732,9 @@ function flux_surfaces(eqt::equilibrium__time_slice{T}, B0::T, R0::T; upsample_f
 
     # secondary separatrix
     psi2nd = find_psi_2nd_separatrix(eqt, PSI_interpolant)
-    (tmp,), _ = flux_surface(r, z, PSI, eqt.profiles_1d.psi, eqt.global_quantities.magnetic_axis.r, eqt.global_quantities.magnetic_axis.z, psi2nd, :encircling)
+    tmp, _ = flux_surface(r, z, PSI, eqt.profiles_1d.psi, eqt.global_quantities.magnetic_axis.r, eqt.global_quantities.magnetic_axis.z, psi2nd, :encircling)
     if !isempty(tmp)
-        (pr2nd, pz2nd) = tmp
+        (pr2nd, pz2nd) = tmp[1]
         eqt.boundary_secondary_separatrix.outline.r = pr2nd
         eqt.boundary_secondary_separatrix.outline.z = pz2nd
     end