Without a running language server (none configured for the language, or not installed, stopped or crashed), the editor showed no syntax errors at all, though the built-in parser already finds them. The editor now reports the parser's errors for such files, checked again after edits and when a language server starts or stops; while a server runs for the language it reports syntax errors itself. SQL is left to the database support. The check is the built-in Syntax errors inspection.
Fixes#824
