fix(com4FlowPy): defining default as fallback

[MunsMan]

I discovered yesterday an edge case in the PRA configuration via input files.
It missed to reapply the default value, if the input files provides an invalid value. In such a case we where reusing the previous value.

Visually, this impacted the results:

before:

after:

PR Checklist

Please confirm before requesting review:

• I ran pytest locally without fails
• I added/updated tests where needed
• I updated documentation where needed

Confirm before the final merge/rebase into master

• Commits are sensibly squashed and rebased onto latest master
• Standardtest run without difference (with recompiled cython code)

[fso42]

Thanks, I'll wait for feedback from @PaulaSp3 or @ahuber-bfw

Sidenote: I you want I can invite you to the OpenNHM Team and you can work directly on the repo... Just let me know

[ahuber-bfw]

• immediate fix for the re-initialisation of parameters in case of missing or invalid values in the input rasters ✓
• as a follow up I would suggest also adapting com4FlowPy.checkInputParameterValues() to check input parameters before the model is run (#1327)