STATISTICS: Calculate current density only if magnetic field present.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>

sources/statistics.F90

@@ -772,10 +772,6 @@ module statistics
         dh(2) = ady(pmeta%level)
         dh(3) = adz(pmeta%level)
 
-! calculate current density (J = ∇xB)
-!
-        call curl(dh(:), pdata%q(ibx:ibz,:,:,:), jc(1:3,:,:,:))
-
 ! total mass
 !
 #if NDIMS == 3
@@ -820,6 +816,11 @@ module statistics
                                     + pdata%q(iby,nb:ne,nb:ne,  :  )**2 &
                                     + pdata%q(ibz,nb:ne,nb:ne,  :  )**2) * dvolh
 #endif /* NDIMS == 3 */
+
+! calculate current density (J = ∇xB)
+!
+          call curl(dh(:), pdata%q(ibx:ibz,:,:,:), jc(1:3,:,:,:))
+
         end if
 
         if (.not. periodic(1)) then