Wcs handle errors

[gbburkhardt]

Description of the Change

• bug fix: request to WCS is clipped to Sector size of data available on the server. Mapserver will return an error if the request is for a region outside of the extent of the layer.
• bug fix: support case insensitive check for DTED extension; data sets exist in which the file extension is in caps.
• add error handling for WCS operations
• avoid memory/resource leaks

Why Should This Be In Core?

Bugs, of course, should be fixed. Memory/resource leaks are "bad". I added the error checks when I was debugging my setup of a WCS server for elevation data. They are likely to help others.

Benefits

more robust code

Potential Drawbacks

I was a bit concerned of the effect clipping the tile size to what's in the server would have on other code in the system. As far as I could tell, the ElevationModel correctly handles missing data, and if a request is made for data outside the clipped tile, the next ElevationModel in the list will be checked.

Applicable Issues

None that I know of...