Add same fix as #3964 to lib/mruby/gem.rb .

lib/mruby/gem.rb

@@ -176,6 +176,7 @@ module MRuby
             f.puts %Q[  mrb_load_irep(mrb, gem_mrblib_irep_#{funcname});]
             f.puts %Q[  if (mrb->exc) {]
             f.puts %Q[    mrb_print_error(mrb);]
+            f.puts %Q[    mrb_close(mrb);]
             f.puts %Q[    exit(EXIT_FAILURE);]
             f.puts %Q[  }]
           end