Address PR comments

Signed-off-by: JCW <a1q123456@users.noreply.github.com>

src/xrpld/core/Coro.ipp

@@ -71,13 +71,13 @@ inline JobQueue::Coro::~Coro()
         "ripple::JobQueue::Coro::~Coro : is finished");
 }
 
-inline void
+inline bool
 JobQueue::Coro::yield()
 {
     {
         std::lock_guard lock(jq_.m_mutex);
         if (shouldStop())
-            return;
+            return false;
 
         state_ = CoroState::Suspended;
         cv_.notify_all();

src/xrpld/core/JobQueue.h

@@ -99,9 +99,11 @@ public:
             Note:
               The associated Job function returns.
               Undefined behavior if called consecutively without a corresponding
-           post.
+              post.
+              It may not suspend at all if the JobQueue is stopping, and returns
+              false in such a case.
         */
-        void
+        bool
         yield();
 
         /** Schedule coroutine execution.
@@ -147,7 +149,7 @@ public:
         join();
 
         /** Returns true if the coroutine should stop executing */
-        bool
+        [[nodiscard]] bool
         shouldStop() const;
     };