Set electron parallel flow equal to the ion one for Boltzmann response

The electron parallel flow is not used when Boltzmann response is used,
but most sensible thing is probably to set zero current. This version
assumes a single ion species, and sets the electron parallel flow equal
to the parallel flow of ion species 1.

moment_kinetics/src/electron_fluid_equations.jl

@@ -111,6 +111,11 @@ function calculate_electron_upar_from_charge_conservation!(upar_e, updated, dens
                 # convert from parallel particle flux to parallel particle density
                 upar_e[iz,ir] /= dens_e[iz,ir]
             end
+        else
+            begin_r_z_region()
+            @loop_r_z ir iz begin
+                upar_e[iz,ir] = upar_i[iz,ir,1]
+            end
         end
         updated[] = true
     end