Graph Toolkit's MiniMap "Zoom" is "NaN" when the Graph is just opened and the zoom wasn't changed

How to reproduce:
1. Create a new Unity project and import the "Graph" Script and "Test" Graph
2. Open the "Test" Graph
3. Make sure the "MiniMap" is enabled
4. Observe the "Zoom" field on MiniMap

Expected results: The zoom is a normal numeric value
Actual results: The zoom is "Nan"

Reproducible with: 6000.4.0b7, 6000.5.0a6

Reproducible on: macOS Tahoe 26 (M1)
Not reproducible on: No other environment tested

Note: Reproducible only if the Placemat wasn't unfocused after creation