Refactor code deciding the kind of span of a grid cell

Move wxGrid's GetCellSize() cell span logic into GetCellSpan() for
future usage.

src/generic/grid.cpp

@@ -158,6 +158,24 @@ wxDEFINE_EVENT( wxEVT_GRID_TABBING, wxGridEvent );
 // implementation
 // ============================================================================
 
+namespace
+{
+
+// Helper function for consistent cell span determination based on cell size.
+wxGrid::CellSpan GetCellSpan(int numRows, int numCols)
+{
+    if ( numRows == 1 && numCols == 1 )
+        return wxGrid::CellSpan_None; // just a normal cell
+
+    if ( numRows < 0 || numCols < 0 )
+        return wxGrid::CellSpan_Inside; // covered by a multi-span cell
+
+    // this cell spans multiple cells to its right/bottom
+    return wxGrid::CellSpan_Main;
+}
+
+} // anonymous namespace
+
 wxIMPLEMENT_ABSTRACT_CLASS(wxGridCellEditorEvtHandler, wxEvtHandler);
 
 wxBEGIN_EVENT_TABLE( wxGridCellEditorEvtHandler, wxEvtHandler )
@@ -9126,14 +9144,7 @@ wxGrid::GetCellSize( int row, int col, int *num_rows, int *num_cols ) const
 {
     GetCellAttrPtr(row, col)->GetSize( num_rows, num_cols );
 
-    if ( *num_rows == 1 && *num_cols == 1 )
-        return CellSpan_None; // just a normal cell
-
-    if ( *num_rows < 0 || *num_cols < 0 )
-        return CellSpan_Inside; // covered by a multi-span cell
-
-    // this cell spans multiple cells to its right/bottom
-    return CellSpan_Main;
+    return GetCellSpan(*num_rows, *num_cols);
 }
 
 wxGridCellRenderer* wxGrid::GetCellRenderer(int row, int col) const