Fix possibility duplicate share for short donation intervals.

src/workers/SingleWorker.h

@@ -41,9 +41,12 @@ public:
     void start() override;
 
 private:
+    bool resume(const Job &job);
     void consumeJob();
+    void save(const Job &job);
 
     Job m_job;
+    Job m_paused;
     JobResult m_result;
 };