Split array declaration from initialization to avoid potential Z shell error

Error is: `local:217: maximum nested function level reached`. This error occurs when $SHELL is started.
Z shell version: `zsh 4.3.17 (x86_64-unknown-linux-gnu)`

Alternative would be to remove `local` keyword, but I assume the variable has no use outside the switch-case.
See http://zshwiki.org/home/scripting/array and http://stackoverflow.com/questions/14917501/local-arrays-in-zsh.

#### Screenshot:
![screenshot of zsh-prompt when loading](https://cloud.githubusercontent.com/assets/3382469/4382862/e498de38-4392-11e4-860d-012e85e45608.png "screenshot of zsh-prompt when loading")