Don't show an error for a failed automatic refresh

Summary:
If it's an automatically triggered refresh, the first time it fails a likely
transient (no network, locking failed, init failed) error is not shown.

Test Plan:
Started zypper in the background, which locks the database.
Reset the timestamp to 0 and started the applet in plasmawindowed.
The first autorefresh error wasn't displayed, but the subsequent ones were.
After quitting zypper it refreshed successfully and the count was reset.

Reviewers: bruns, antlarr

Differential Revision: https://phabricator.kde.org/D27423