Duplicate Image ID

A single file node was connected to the color attribute
of two different shaders.

When exported, there are two image ids which are identical.

<library_images>
<image id="file1-image" name="file1">
<init_from>./texture.tga</init_from>
</image>
<image id="file1-image" name="file1">
<init_from>./texture.tga</init_from>
</image>
</library_images>

To be legal XML, each image needs a unique ID.

See attachment for an example.