Generalize the constraint on `dist_lim`

For a non-uniform longitude-latitude grid. As in `input_ssh` for
`max_radius(1)`. See commit 803b9bcc.

Overlap/config_graph.F90

@@ -30,9 +30,9 @@ contains
 #ifndef CPP_SEQUENTIAL
     use ezmpi, only: ezmpi_bcast
 #endif
-    use jumble, only: assert, pi
+    use jumble, only: assert
 
-    use read_grid_m, only: periodic, step
+    use read_grid_m, only: periodic, nlon
 
     integer, intent(in):: rank
 
@@ -49,8 +49,7 @@ contains
        read(unit = *, nml = config_graph_nml)
        write(unit = *, nml = config_graph_nml)
        call assert(max_delta >= 1, "config_graph max_delta")
-       if (periodic) call assert(2 * dist_lim * step(1) < PI, &
-            "config_graph dist_lim")
+       if (periodic) call assert(4 * dist_lim < nlon, "config_graph dist_lim")
        copy = merge(dist_lim, 0, periodic)
     end if