DataTable curser doesn't move properly on mono

#### Issue details
Run MissionPlanner on mono, Review DataFlash Log, Show DataTable, graph any variable, double click on the graph to select specific point, the DataTable curser doesn't move according.
It should move to the specific line as the point on graph.

#### Version
_MP 1.3.68_ Cannot remember if it was working previously.

#### Platform
[ x ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

Reproduce the issue in Mission Planner on mono by opening a DataFlash Log, showing the DataTable, graphing a variable, and double-clicking a graph point. Start by tracing the DataTable and graph interaction; done means the DataTable cursor moves to the line corresponding to the selected graph point.

Written by the indexing model from the issue text.