Fix reporting of an error during error handling.

Reported by Sergey Kaplun. #1381

src/lj_err.c

@@ -803,9 +803,17 @@ LJ_NOINLINE GCstr *lj_err_str(lua_State *L, ErrMsg em)
   return lj_str_newz(L, err2msg(em));
 }
 
+LJ_NORET LJ_NOINLINE static void lj_err_err(lua_State *L)
+{
+  setstrV(L, L->top++, lj_err_str(L, LJ_ERR_ERRERR));
+  lj_err_throw(L, LUA_ERRERR);
+}
+
 /* Out-of-memory error. */
 LJ_NOINLINE void lj_err_mem(lua_State *L)
 {
+  if (L->status == LUA_ERRERR)
+    lj_err_err(L);
   if (L->status == LUA_ERRERR+1)  /* Don't touch the stack during lua_open. */
     lj_vm_unwind_c(L->cframe, LUA_ERRMEM);
   if (LJ_HASJIT) {
@@ -902,6 +910,8 @@ LJ_NOINLINE void LJ_FASTCALL lj_err_run(lua_State *L)
 /* Stack overflow error. */
 void LJ_FASTCALL lj_err_stkov(lua_State *L)
 {
+  if (L->status == LUA_ERRERR)
+    lj_err_err(L);
   lj_debug_addloc(L, err2msg(LJ_ERR_STKOV), L->base-1, NULL);
   lj_err_run(L);
 }

src/lj_state.c

@@ -195,6 +195,7 @@ static TValue *cpluaopen(lua_State *L, lua_CFunction dummy, void *ud)
   lj_meta_init(L);
   lj_lex_init(L);
   fixstring(lj_err_str(L, LJ_ERR_ERRMEM));  /* Preallocate memory error msg. */
+  fixstring(lj_err_str(L, LJ_ERR_ERRERR));  /* Preallocate err in err msg. */
   g->gc.threshold = 4*g->gc.total;
 #if LJ_HASFFI
   lj_ctype_initfin(L);