gtk_image_new_from_file fails on Windows for SVG

[Richard Shann <richard rshann plus com>]

For a long time now I have been working around 
gtk_image_new_from_file ()

not working on windows trying to load SVG images. Instead I have used

pb = rsvg_pixbuf_from_file (filename, &err);

and then

gtk_image_new_from_pixbuf (pb)

and this works for some SVG images. However, even this is failing for
the SVG files generated by LilyPond, it generates an image with only the
background color.

I thought this might be due to the use of the syntax "currentColor" but
changing this to "black" did not help. I also noticed that rsvg library
has a change log entry for fixing rgb color parsing, so avoided that
syntax, but I still can't get the images to load on Windows. The Gtk
version being built (and run) against is 3.6.5 
Any suggestions what might be causing the trouble in LilyPond's output?

Richard