Read `main_nml` before `n_slices`

Because we are going to introduce the choice of a slice in the namelist.

Overlap/eddy_graph.f90

@@ -47,6 +47,12 @@ program eddy_graph
   call config_graph(rank)
 
   if (rank == 0) then
+     ! main_nml:
+     write(unit = *, nml = main_nml)
+     print *, "Enter namelist main_nml."
+     read(unit = *, nml = main_nml)
+     write(unit = *, nml = main_nml)
+
      ! n_slices:
 
      call new_unit(unit)
@@ -62,11 +68,6 @@ program eddy_graph
         n_slices = 1
      end if
 
-     ! main_nml:
-     write(unit = *, nml = main_nml)
-     print *, "Enter namelist main_nml."
-     read(unit = *, nml = main_nml)
-     write(unit = *, nml = main_nml)
      call assert(n_dates == huge(0) .or. n_slices == 1, "If we have several " &
           // "slices then we read all the dates from them")
   end if