Work around problems with autorandr's completion when using `bashcompinit`
On ZSH the easiest approach to get bash completions running is to use
`bashcompinit`. Unfortunately it seems as there are slight differences
between ZSH and bash which cause problems when using that feature.
I had to change the following things:
* Replace the `-n` check with a length check of the AR directory array:
ZSH adds an empty string at first if no system directory for autorandr
was found. Checking if there's at least a single element works around
this problem.
* Silence errors from `find`. The empty string at first causes a
`directory not found error` during the completion.
It can be tested on ZSH after running the following command: