bug: Slope selector crashes when PK parameters are removed

[Shaakon35]

Description

The slope selector crashes when certain PK parameters are deselected. It depends too heavily on the selected PK parameters and should be more resilient.

Steps to Reproduce

Use the dummy data pre-loaded in the app by default.

1. Select Drug A only
2. Remove all PK parameters for Multiple IV Bolus
3. Check the slope selector — it works fine

Then try removing parameters one at a time from this list:

• R2ADJ
• CLST
• CLSTD
• CMAX
• CMAXD
• LAMZHL
• LAMZ
• LAMZNPT
• LAMZLL
• R2
• LAMZSPN
• TLST
• TMAX
• VSSO

Removing just one parameter causes the slope selector to crash.

Expected Behavior

The slope selector should not crash when PK parameters are removed. It should not rely so heavily on most PK parameters being selected.

Fix Needed

The slope selector plot function needs to be fixed so it does not depend on the full set of PK parameters being present.