Corrected call to open_file in open_restart_units

  Corrected the arguments in a call to open_file in open_restart_units when the
restart files are decomposed using the IO-layout.  All answers are bitwise
identical, but this fixes an error later on if this unit handle is used to read
from such a set of decomposed restart files.

src/SIS_restart.F90

@@ -315,7 +315,8 @@ function open_restart_units(filename, directory, domain, CS, IO_handles, file_pa
           if (fexists) then
             nf = nf + 1
             if (present(IO_handles)) &
-              call open_file(IO_handles(nf), trim(filepath), READONLY_FILE, MOM_domain=domain)
+              call open_file(IO_handles(nf), trim(filepath), READONLY_FILE, MOM_domain=domain, &
+                             threading=MULTIPLE, fileset=MULTIPLE)
             if (present(global_files)) global_files(nf) = .false.
             if (present(file_paths)) file_paths(nf) = filepath
           endif