Do not leak Future when CompanionTransportManager.sendMessage() thows

Remove CompletableFuture callback object from mPendingRequests if
sendMessage() throws an IOException.

Bug: 237030169
Test: atest CompanionTests
Change-Id: I067cc5f1b7b86a20d2bf74229d6bd9c5fda74e35

services/companion/java/com/android/server/companion/transport/CompanionTransportManager.java

@@ -200,6 +200,9 @@ public class CompanionTransportManager {
             try {
                 sendMessage(message, sequence, data);
             } catch (IOException e) {
+                synchronized (mPendingRequests) {
+                    mPendingRequests.remove(sequence);
+                }
                 pending.completeExceptionally(e);
             }
             return pending;