Gets the base size for the icon. The base size is a size for the icon that was specified by the icon theme creator. This may be different than the actual size of image; an example of this is small emblem icons that can be attached to a larger icon. These icons will be given the same base size as the larger icons to which they are attached.
[integer] the base size, or 0, if no base size is known for the icon.
Derived by RGtkGen from GTK+ documentation