Fix are_adjacent() method

Next incidence was not updated correctly, which could lead to bad results and infinite loops.

src/main.rs

@@ -33,16 +33,17 @@ impl Graph {
 
     // TODO: 'fn are_adjacent()' could probably be done with a neighbor vertex iterator.
     fn are_adjacent(&self, v1: Vertex, v2: Vertex) -> bool {
-        let Some(next) = self.vertex_incidence_headers[v1.0].first_incidence else {
+        let Some(mut incidence) = self.vertex_incidence_headers[v1.0].first_incidence else {
             return false;
         };
         loop {
-            if self.incidence_vertices[next.0] == v2 {
+            if self.incidence_vertices[incidence.0] == v2 {
                 return true;
             }
-            let Some(next) = self.next_incidences[next.0] else {
+            let Some(next) = self.next_incidences[incidence.0] else {
                 return false;
             };
+            incidence = next;
         }
     }