Update Workflow.h

Author: Barenboim

src/factory/Workflow.h

@@ -241,6 +241,8 @@ class ParallelWork : public ParallelTask
 	{
 		if (index < this->subtasks_nr)
 			return this->all_series[index];
+		else
+			return NULL;
 	}
 
 	SeriesWork& operator[] (size_t index)
@@ -257,10 +259,10 @@ class ParallelWork : public ParallelTask
 
 public:
 	SeriesWork *begin() { return this->series_at(0); }
-	SeriesWork *end() { return this->series_at(this->size()); }
+	SeriesWork *end() { return this->all_series + this->subtasks_nr;}
 
-	const SeriesWork *begin() const { return this->series_at(0); }
-	const SeriesWork *end() const { return this->series_at(this->size()); }
+	const SeriesWork *begin() const { return this->series_at(0);}
+	ccons 	SeriesWork *end() const { return this->all_series + this->subtasks_nr;}
 
 public:
 	void set_callback(parallel_callback_t callback)