fix wandering empty diagnostic highlights

The last commit introduces support for highlighting empty selections
by properly calculating their vis ranges.
However File:content does return an empty string for empty ranges
and we can not check whether the diagnostic still applies to the same
position.

This is fixed by faking a one character range when receiving an
empty one.
Doing so we get a valid one-character content we can compare and
still have proper highlighting because we unconditionally decrement
the range end in highlight_diagnostics.

Fixes: 7099e56062861fc8dbb143e78447cce6bf886a97

0 files changed, 0 insertions, 0 deletions