Fix wxGrid::SetColSize for the native header

In case of the width of -1 for the native header the title width must be
calculated by the native header itself.

src/generic/grid.cpp

@@ -9127,6 +9127,12 @@ void wxGrid::SetColSize( int col, int width )
     // make the code more complex), and for them passing -1 simply means to
     // show the column back using its old size.
     if ( width == -1 && GetColWidth(col) != 0 )
+    {
+        if ( m_useNativeHeader )
+        {
+            width = GetGridColHeader()->GetColumnTitleWidth(col);
+        }
+        else
         {
             long w, h;
             wxArrayString lines;
@@ -9138,6 +9144,7 @@ void wxGrid::SetColSize( int col, int width )
             else
                 GetTextBoxSize( dc, lines, &h, &w );
             width = w + 6;
+        }
 
         // Check that it is not less than the minimal width and do use the
         // possibly greater than minimal-acceptable-width minimal-width itself