Use graph::reset() to Reset a Canceled Graph

When a graph execution is canceled either because of an unhandled exception or because its task_group_context is canceled explicitly, the graph and its nodes may be left in an indeterminate state. For example, in the code samples shown in Cancel a Graph Explicitly the input 2 may be left in a buffer. But even beyond remnants in the buffers, there are other optimizations performed during the execution of a flow graph that can leave its nodes and edges in an indeterminate state. If you want to re-execute or restart a graph, you first need to reset the graph:

try {
    g.wait_for_all();
} catch ( int j ) {
    cout << "Caught " << j << "\n";
    // do something to fix the problem
    g.reset();
    f1.try_put(1);
    f1.try_put(2);
    g.wait_for_all();
}