Don't get stuck when exiting Clementine while library is being created/updated

ext/libclementine-common/core/workerpool.h

@@ -191,6 +191,10 @@ WorkerPool<HandlerType>::~WorkerPool() {
       }
     }
   }
+
+  foreach (ReplyType* reply, message_queue_) {
+    reply->Abort();
+  }
 }
 
 template <typename HandlerType>

src/library/library.cpp

@@ -101,7 +101,7 @@ Library::Library(Application* app, QObject *parent)
 Library::~Library() {
   watcher_->deleteLater();
   watcher_thread_->exit();
-  watcher_thread_->wait();
+  watcher_thread_->wait(5000 /* five seconds */);
 }
 
 void Library::Init() {