avoid segfaults when accessing lammps_last_thermo()

src/library.cpp

@@ -858,14 +858,17 @@ void *lammps_last_thermo(void *handle, const char *what, int index)
 {
   auto lmp = (LAMMPS *) handle;
   void *val = nullptr;
+
+  if (!lmp->output) return val;
   Thermo *th = lmp->output->thermo;
-  if (!th) return nullptr;
+  if (!th) return val;
   const int nfield = *th->get_nfield();
 
   BEGIN_CAPTURE
   {
     if (strcmp(what, "setup") == 0) {
-      val = (void *) &lmp->update->setupflag;
+      if (lmp->update)
+        val = (void *) &lmp->update->setupflag;
 
     } else if (strcmp(what, "line") == 0) {
       val = (void *) th->get_line();