Fix panic in pad node

src/geom/length.rs

@@ -126,6 +126,13 @@ impl Length {
     pub fn approx_eq(self, other: Self) -> bool {
         self == other || (self - other).to_raw().abs() < 1e-6
     }
+
+    /// Perform a checked division by a number, returning `None` if the result
+    /// is not finite.
+    pub fn div_finite(self, number: f64) -> Option<Self> {
+        let result = self.to_raw() / number;
+        result.is_finite().then(|| Self::raw(result))
+    }
 }
 
 impl Debug for Length {

src/layout/pad.rs

@@ -25,7 +25,9 @@ impl BlockLevel for PadNode {
             frames.iter_mut().zip(regions.iter())
         {
             fn solve_axis(length: Length, padding: Linear) -> Length {
-                (length + padding.abs) / (1.0 - padding.rel.get())
+                (length + padding.abs)
+                    .div_finite(1.0 - padding.rel.get())
+                    .unwrap_or_default()
             }
 
             // Solve for the size `padded` that satisfies (approximately):

tests/typ/layout/pad.typ

@@ -27,9 +27,11 @@ Hi #box(pad(left: 10pt)[]) there
 
 ---
 // Test that the pad node doesn't consume the whole region.
-
 #page(height: 6cm)
-
 #align(left)[Before]
 #pad(10pt, image("../../res/tiger.jpg"))
 #align(right)[After]
+
+---
+// Test that padding adding up to 100% does not panic.
+#pad(50%)[]