Fix: Preserve order of selected values in multiselect / listbox (multiple) TVs

Fixes issue: https://github.com/modxcms/revolution/issues/9206

before:
![bildschirmfoto 2014-06-24 um 18 50 20](https://cloud.githubusercontent.com/assets/445501/3374556/d0eba49e-fbbf-11e3-959d-746381d4c4c2.png)

after:
![bildschirmfoto 2014-06-24 um 19 50 31](https://cloud.githubusercontent.com/assets/445501/3375277/18258304-fbc8-11e3-9050-05dc1bc8ff39.png)