When user installs a dev/beta/alpha/rc version (e.g. 4.25.0-dev),
check_update would skip prerelease releases and compare against the
latest stable (e.g. 4.24.0). Since 4.25.0-dev > 4.24.0 in semver
comparison (numeric part takes precedence), it incorrectly prompted
to update.
Now checks if current version is prerelease and already newer than
the latest stable - in that case, no update prompt is shown.
Fixes: update button shown to users running dev/unstable versions