Run VM events and finalizers in separate state.

Reported by Sergey Kaplun. #1403

src/lj_vmevent.c

@@ -38,6 +38,7 @@ ptrdiff_t lj_vmevent_prepare(lua_State *L, VMEvent ev)
 void lj_vmevent_call(lua_State *L, ptrdiff_t argbase)
 {
   global_State *g = G(L);
+  lua_State *oldL = gco2th(gcref(g->cur_L));
   uint8_t oldmask = g->vmevmask;
   uint8_t oldh = hook_save(g);
   int status;
@@ -51,6 +52,10 @@ void lj_vmevent_call(lua_State *L, ptrdiff_t argbase)
     fputs(tvisstr(L->top) ? strVdata(L->top) : "?", stderr);
     fputc('\n', stderr);
   }
+  setgcref(g->cur_L, obj2gco(oldL));
+#if LJ_HASJIT
+  G2J(g)->L = oldL;
+#endif
   hook_restore(g, oldh);
   if (g->vmevmask != VMEVENT_NOCACHE)
     g->vmevmask = oldmask;  /* Restore event mask, but not if not modified. */