Fix validation check in Cycle

It didn't do the check, if the cycle had only one edge.

crates/fj-kernel/src/objects/cycle.rs

@@ -53,6 +53,7 @@ impl Cycle {
                     "Edges in cycle do not connect"
                 );
             }
+        }
 
         // Verify that the edges form a cycle
         if let Some(first) = half_edges.first() {
@@ -67,7 +68,6 @@ impl Cycle {
                 );
             }
         }
-        }
 
         Self {
             surface,