Fix testing range-selection

The previous commit reveals a bug in the grid test where the
wxEVT_GRID_RANGE_SELECTED detected is not really comming from
range selection action, but from the grid cursor changing its position

For unknown reasons, range selection in the test doesn't really starts off
unless we move the mouse first while still inside the first selected cell

tests/controls/gridtest.cpp

@@ -674,6 +674,11 @@ TEST_CASE_METHOD(GridTestCase, "Grid::RangeSelect", "[grid]")
     sim.MouseDown();
     wxYield();
 
+    // Move the mouse a bit while staying inside the first cell of the range
+    // so that the range selection really starts off by the next move.
+    sim.MouseMove(pt.x + 5, pt.y + 5);
+    wxYield();
+
     sim.MouseMove(pt.x + 50, pt.y + 50);
     wxYield();