`tap run`: wrong path handling for the csv parameter file

Check for example:

$ tap run parameter.TapPlan -e parameter.csv
OpenTAP Command Line Interface 9.13.0+a5998b9e

Loaded test plan from /home/user/parameter.TapPlan [37.5 ms]
Loading external parameters from 'parameter.csv'.
Caught error while loading test plan: 'Could not find file
'/home/user/.tap/parameter.csv'.'