A document indexer that anchors a whole-file definition at the file's start
(an empty range at 0:0) had the whole document rejected with "invalid
navigation anchors". Empty ranges inside the document are now accepted:
Go to Declaration lands on them, while Find Usages and Rename skip them so
a rename never inserts the new name at that position. The error for a
document that is still rejected names the plugin and the file.