vcl: Image: mark newly added constructor "explicit"

Change-Id: I6d114e932d113f3d126cac3f7e43fade2a740245

include/vcl/image.hxx

@@ -58,7 +58,7 @@ public:
                     Image( const Bitmap& rBitmap, const Bitmap& rMaskBitmap );
                     Image( const Bitmap& rBitmap, const Color& rColor );
                     Image( const ::com::sun::star::uno::Reference< ::com::sun::star::graphic::XGraphic >& rxGraphic );
-                    Image( const OUString &rFileUrl );
+                    explicit Image( const OUString &rPNGFileUrl );
                     ~Image();
 
     Size            GetSizePixel() const;