Edit the current wxGrid selection block

Really edit the current selection block instead of storing the temporary
information about the current selection and applying it on releasing Shift
key or LKM.

include/wx/generic/private/grid.h

@@ -793,6 +793,19 @@ public:
     // boundary, i.e. is the first/last row/column
     virtual bool IsAtBoundary(const wxGridCellCoords& coords) const = 0;
 
+    // Check if the component of this point in our direction is
+    // valid, i.e. not -1
+    bool IsValid(const wxGridCellCoords& coords) const
+    {
+        return m_oper.Select(coords) != -1;
+    }
+
+    // Make the coordinates with the other component value of -1.
+    wxGridCellCoords MakeWholeLineCoords(const wxGridCellCoords& coords) const
+    {
+        return m_oper.MakeCoords(m_oper.Select(coords), -1);
+    }
+
     // Increment the component of this point in our direction
     virtual void Advance(wxGridCellCoords& coords) const = 0;