pcbnew: Disable capture cursor in measure tool

When starting the measure tool, the cursor should not be captured until
we begin the measurement.

Fixes: lp:1806486
* https://bugs.launchpad.net/kicad/+bug/1806486

pcbnew/tools/edit_tool.cpp

@@ -1225,6 +1225,7 @@ int EDIT_TOOL::MeasureTool( const TOOL_EVENT& aEvent )
 
     controls.ShowCursor( true );
     controls.SetAutoPan( false );
+    controls.CaptureCursor( false );
 
     while( auto evt = Wait() )
     {