Created Unassigned: Not all drawings are loaded from a sheet [15028]

Several sheets that I work with only have AlternateContent nodes. The code in ExcelDrawings.cs (AddDrawing) iterates all child nodes of the xdr:wsDr node looking for one of the following:
* oneCellAnchor
* twoCellAnchor
* absoluteAnchor

The commented out line:
```
//XmlNodeList list = _drawingsXml.SelectNodes("//mc:Choice/xdr:twoCellAnchor", NameSpaceManager);

```
indicates that you were originally looking for an anchor node anywhere in the content. I made the following change (to my version of 4.0.1) which seems to work fine with the AlternateContent nodes:

```
XmlNodeList list = _drawingsXml.SelectNodes("//mc:Choice/*[self::xdr:twoCellAnchor or self::xdr:oneCellAnchor or self::xdr:absoluteAnchor]", NameSpaceManager);

```
Then the foreach loop can make use of this list.
Thanks
Paul.