gr_basic.cpp: ensure a pen with width = 0 is transparent.

Setting its color to COLOR4D::UNSPECIFIED (i.e. opacity = 0) is not enough
for all  platforms (i.e. Windows)
From master branch
Fixes #14915
https://gitlab.com/kicad/code/kicad/-/issues/14915

common/gr_basic.cpp

@@ -94,7 +94,10 @@ void GRSetColorPen( wxDC* DC, const COLOR4D& Color, int width, wxPenStyle style
     // wxWidgets will enforce a minimum pen width when printing, so we have to make the pen
     // transparent when we don't want the object stroked.
     if( width == 0 )
+    {
         color = COLOR4D::UNSPECIFIED;
+        style = wxPENSTYLE_TRANSPARENT;
+    }
 
     const wxPen& curr_pen = DC->GetPen();