Fixes two bugs related to opening an ObjectPanel when there is no data flowing in

1. Fixes an issue that caused the panel to not draw itself correctly until the mouse moved over it when there was previously data flowing and it had then stopped (ie when playing a log, and then pausing to view the data).

2. Fixes an issue where requesting a large graph when the user had seen data, but the data flow had now stopped hung the application.

3. (minor) Fixes an issue where axis ranges were computed incorrectly when there was only one point on the graph.