Empty ranges are valid in lsp

Empty ranges are valid in lsp

The previous hack in eglot--range-region, designed to appease cquery's
occasional practice of publishing diagnostics with empty regions, was
moved to the proper notification handler.

Reported by mkcms <k.michal@zoho.com>.

* eglot.el (eglot--range-region): Allow empty ranges, which are
allowed in LSP.
(eglot-handle-notification :textDocument/publishDiagnostics): Maybe
fallback to flymake-diag-region here.

GitHub-reference: close https://github.com/joaotavora/eglot/issues/27