fix: cleanup also the Pending related subs

earlier commit already included cleanup for the Ready and Cancelled
cases and this will do the same for Pending cases. the end result
doesn't change but as is apparent from the test changes: a single
Some(0) becomes None. however this does remove leaking and potential
bugs when a previously completed subscription would be reused.

src/subscription.rs

@@ -369,13 +369,20 @@ impl<TRes: Debug + PartialEq> Drop for SubscriptionFuture<TRes> {
             // check if this is the last subscription to this resource
             let is_last = related_subs.is_empty();
 
+            if is_last {
+                subscriptions.remove(&self.kind);
+            }
+
             (sub, is_last)
         });
 
         if let Some(sub) = sub {
             // don't bother updating anything that isn't `Pending`
             if let mut sub @ Subscription::Pending { .. } = sub {
-                debug!("It was the last related subscription, sending a cancel notification");
+                debug!(
+                    "Last related subscription dropped, sending a cancel notification for {} to {}",
+                    self.id, self.kind
+                );
                 sub.cancel(self.kind.clone(), is_last);
             }
         }

tests/wantlist_and_cancellation.rs

@@ -43,7 +43,8 @@ async fn check_cid_subscriptions(ipfs: &Node, cid: &Cid, expected_count: usize)
         assert_eq!(subs.len(), 1);
     }
     let subscription_count = subs.get(&cid.clone().into()).map(|l| l.len());
-    assert_eq!(subscription_count, Some(expected_count));
+    // treat None as 0
+    assert_eq!(subscription_count.unwrap_or(0), expected_count);
 }
 
 /// Check if canceling a Cid affects the wantlist.