DTED formats dt0 and dt1 DnD fix

public URL createConnectionURL( Object context ) {
URL url = CatalogPlugin.locateURL(context);

if (url == null) {
return null;
}

url = checkedURL(url);
if (url == null || url.getFile() == null) {
return null;
}

// Checks whether file is acceptable based on extension.
String fileExt = url.getFile().substring(url.getFile().lastIndexOf('.') + 1);
if (fileExt != null)
fileExt = fileExt.toLowerCase();

for( String extensionsForFile : getExtensionList() ) {
extensionsForFile = extensionsForFile.toLowerCase();
String[] validExtensions = extensionsForFile.split(",");
for (String validExtension : validExtensions) {
if (fileExt.equals(validExtension.substring(validExtension.lastIndexOf('.') + 1))) {
// actually do a test
File f = URLUtils.urlToFile(url);
if (f.exists())
return url;
}
}
}
return null;
}