Fix non-terminating loop in flow layout (#3652)

crates/typst/src/layout/flow.rs

@@ -257,9 +257,15 @@ impl<'a> FlowLayouter<'a> {
 
                 let carry: Vec<_> = self.items.drain(sticky..).collect();
                 self.finish_region(engine, false)?;
+                let in_last = self.regions.in_last();
+
                 for item in carry {
                     self.layout_item(engine, item)?;
                 }
+
+                if in_last {
+                    break;
+                }
             }
         }
 

tests/typ/bugs/3641-float-loop.typ

@@ -0,0 +1,11 @@
+// Flow layout should terminate!
+// https://github.com/typst/typst/issues/3641
+//
+// This is not yet ideal: The heading should not move to the second page, but
+// that's a separate bug and not a regression.
+
+---
+#set page(height: 40pt)
+
+= Heading
+#lorem(6)