Never crash: Fix defringe radius overflow for amounts past the sliders

Treat the amount as the slider's end and keep the radius within the picture.

docs/whats-new.md

@@ -2,6 +2,10 @@
 
 ## 2026-10-13
 
+### Reliability
+- A photo whose Defringe amount was stored far past the sliders' 20 (in a damaged catalog or sidecar) no longer
+  crashes LightCraft each time it renders: the amount acts as 20.
+
 ### Slider drags on large raws
 - Dragging a slider no longer re-renders the edited photo's filmstrip thumbnail on every frame; it follows once you
   let go. On a 64 MP raw the first of those renders decoded the whole file again, which held up the loupe's