Blend Tree Threshold fields accepts NaN/Infinity values causing Node backgrounds disappear in Animator Controller view

Steps to reproduce:
1. Create new Unity project using Universal 3D Template
2. In Project window create Animator Controller and open it
3. Press “+” to create New Layer
4. Right-click on an empty space in the Animator Controller view
5. Select Create State > From New Blend Tree from the context menu
6. Double-click the Blend Tree to enter the Blend Tree Graph
7. Right-click on Blend Tree node and select Add Tree Blend from the context menu
8. Select newly created BlendTree Node
9. In Inspector window > Motion press “+” and select “New Blend Tree” two times
10. Disable “Automate Tresholds” in Inspector window
11. In Motion > BlendTree > Threshold change value from “1” to “NaN”
12. Observe the BlendTree Node in Blend Tree view

Actual results: NaN and Infinity values are accepted and stored, Blend Tree Nodes background disappear in Animator Controller window view

Expected results: NaN and Infinity values are rejected and reverted back to previous valid value, Nodes backgrounds are not affected

Reproducible with versions: 6000.0.74f1, 6000.3.16f1, 6000.4.8f1, 6000.5.0b9, 6000.6.0a5

Tested on (OS): macOS Tahoe 26.4.1