Fix associated false test (!81)

## What is the bug
Fix a test for the if_associated subroutine.
## How do you fix it
The false test did not pop up because of a bug in FortUTF. See #18



Approved-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Merged-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Changelog: bugfix