#386 QwtPicker trackerPosition

[Anonymous]

Hi,
There appears to be a minor bug in QwtPicker when the tracker is enabled. The tracker position is only updated in QwtPicker::widgetMouseMoveEvent, but not in QwtPicker::widgetMousePressEvent. As a result, the tracker can sometimes appear in the wrong location with incorrect coordinates.
To reproduce the issue:

1. Set up a plot with both a picker and a zoomer.
2. Click anywhere to activate the picker's tracker.
3. Zoom the plot.
4. Click again (without moving the mouse) to activate the picker's tracker.
   In this case, the tracker will appear at the "previous" position instead of the new one.
   Note: The tracker position is also updated in QwtPicker::begin(), but only if the tracker position hasn’t been initialized yet.