Roxie activity reset without stop

Found when investigating a memory leak.

Run example aggds1 without running setup.

• An exception is thrown when the file cannot be found
• That is caught in CRoxieContext::executeGraph()
• That calls endGraph - which calls graph->reset()
  STATE: activity 3 reset without stop
• That is caught in endGraph, and then thrown - caussing the original exception to be leaked.

The leak can be fixed by not throwing error if aborting, but a similar error could occur in other situations, and it might be worth thinking about fixing it better.