another workaround for rerun

src/dump.h

@@ -19,6 +19,7 @@
 namespace LAMMPS_NS {
 
 class Dump : protected Pointers {
+ friend class Output;
  public:
   char *id;                // user-defined name of Dump
   char *style;             // style of Dump

src/output.cpp

@@ -632,7 +632,7 @@ int Output::check_time_dumps(bigint ntimestep)
  {
    next_dump_any = MAXBIGINT;
    for (int idump = 0; idump < ndump; idump++)
-     if ((last_dump[idump] >= 0) && !update->whichflag)
+     if ((last_dump[idump] >= 0) && !update->whichflag && !dump[idump]->multifile)
        error->all(FLERR, "Cannot reset timestep with active dump - must undump first");
 
    if (restart_flag_single) {