Fix harmless unused variable warning in wxPropertyGrid code.

Declare variable only used #if wxPG_DOUBLE_BUFFER inside the #if.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62400 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/propgrid/propgrid.cpp

@@ -1982,13 +1982,13 @@ int wxPropertyGrid::DoDrawItems( wxDC& dc,
     long windowStyle = m_windowStyle;
 
     int xRelMod = 0;
-    int yRelMod = 0;
 
     //
     // With wxPG_DOUBLE_BUFFER, do double buffering
     // - buffer's y = 0, so align drawRect and coordinates to that
     //
 #if wxPG_DOUBLE_BUFFER
+    int yRelMod = 0;
 
     wxRect cr2;