tree cache: correctly handle invalidated trees The fix introduced in a02fc2cd1 (2011-05-24; index: correctly parse invalidated TREE extensions) threw out the rest of the data in the extension if it found an invalidated entry. This was the result of incorrect reading of the documentation. Insted, keep reading the extension, as there may be cached data we can use. Signed-off-by: Carlos Martín Nieto <cmn@elego.de>