Fix reporting of an error during error handling.

Reported by Sergey Kaplun. #1381

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);