Avoid compile error and return a value from StartDoc

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@49369 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/dcgraph.cpp

@@ -142,7 +142,8 @@ void wxGCDC::DoDrawIcon( const wxIcon &icon, wxCoord x, wxCoord y )
 }
 
 bool wxGCDC::StartDoc( const wxString& WXUNUSED(message) ) 
-{ 
+{
+    return false;
 }
 
 void wxGCDC::EndDoc()