fix compiler errors

src/input.cpp

@@ -27,9 +27,11 @@
 #include "dihedral.h"
 #include "domain.h"
 #include "error.h"
+#include "fix.h"
 #include "force.h"
 #include "group.h"
 #include "improper.h"
+#include "integrate.h"
 #include "kspace.h"
 #include "memory.h"
 #include "min.h"
@@ -1841,11 +1843,12 @@ void Input::timestep()
   update->dt = utils::numeric(FLERR,arg[0],false,lmp);
   update->dt_default = 0;
 
-  if (update->first_update == 0) return;
-
+  // timestep command can be invoked between runs or by run every
   // calls to other classes that need to know timestep size changed
   // similar logic is in FixDtReset::end_of_step()
-  // only if a run has already occurred
+  // only need to do this if a run has already occurred
+
+  if (update->first_update == 0) return;
 
   int respaflag = 0;
   if (utils::strmatch(update->integrate_style, "^respa")) respaflag = 1;