message: don't pass negative line numbers to Position
diff: @@ -31,7 +31,8 @@ export class LeanDiagnosticsProvider implements Disposable {
  const docMap = new Map<string, TextDocument>();
  for (const message of messages) {
  - const pos = new Position(message.pos_line - 1, message.pos_col);
  + const line = Math.max(message.pos_line - 1, 0);
  + const pos = new Position(line, message.pos_col);
  // Assign the diagnostic to the entire word following the info message
  // so that code actions can be activated more easily
  let msgDoc = docMap.get(message.file_name);
  