Fix duplicate stream check in mpas_stream_list_insert

Fixed a bug in the mpas_stream_list_insert subroutine (in
MPAS_stream_list.F), where the duplicate stream check would fail if
the duplicate stream being inserted was adjacent to its duplicate.
The updated logic ensures that all nodes, including the last, are
checked before insertion.

Author: amstokely

src/framework/mpas_stream_list.F

@@ -118,12 +118,16 @@ subroutine MPAS_stream_list_insert(list, stream, ierr) !{{{
             list % head => stream
         else
             node => list % head
-            do while (associated(node % next))
+            do while (associated(node))
                 if (node % name == stream % name) then
                     if (present(ierr)) ierr = MPAS_STREAM_LIST_DUPLICATE
                     LIST_ERROR_WRITE('Found duplicate item '//trim(stream % name)//' in list.')
                     return
                 end if
+                if (.not. associated(node % next)) then
+                    node % next => stream
+                    exit
+                end if
                 node => node % next
             end do
             node % next => stream