message: [sqllab] fix wrong error msg
  I was getting some "Could not connect to server" when there was
  a proper json payload with an `error` key, the change here makes sure to
  prioritize those messages over the generic one.
diff: @@ -153,10 +153,12 @@ export function runQuery(query) {
  msg = err.responseText;
  }
  }
  - if (textStatus === 'error' && errorThrown === '') {
  - msg = t('Could not connect to server');
  - } else if (msg === null) {
  + if (msg === null) {
  + if (errorThrown) {
  msg = `[${textStatus}] ${errorThrown}`;
  + } else {
  + msg = t('Unknown error');
  + }
  }
  if (msg.indexOf('CSRF token') > 0) {
  msg = t('Your session timed out, please refresh your page and try again.');
  