GtkIconCache: find_image_offset() return 0 if icon_name is NULL.
This avoid a crash calling gtk_about_dialog_set_logo_icon_name() with a NULL icon_name.
GtkAboutDialog: fixed calling gtk_about_dialog_set_logo_icon_name()
with a NULL icon_name. Now it will actually use the default
window icon set as mention in the docs
build/win32/vs*/README.txt: Re-word a bit

Use PATH rather than path to make things clearer