lib/upgrade: Always return latest version, even if older than current (fixes #4654)

The only special check remaining is the one to prefer a minor upgrade
over a major one.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4672

lib/upgrade/upgrade_supported.go

@@ -134,34 +134,25 @@ func SelectLatestRelease(rels []Release, current string, upgradeToPreReleases bo
 
 	var selected Release
 	for _, rel := range rels {
-		switch CompareVersions(rel.Tag, current) {
-		case Older, MajorOlder:
-			// This is older than what we're already running
-			continue
-
-		case MajorNewer:
+		if CompareVersions(rel.Tag, current) == MajorNewer {
 			// We've found a new major version. That's fine, but if we've
 			// already found a minor upgrade that is acceptable we should go
 			// with that one first and then revisit in the future.
 			if selected.Tag != "" && CompareVersions(selected.Tag, current) == Newer {
 				return selected, nil
 			}
-			// else it may be viable, do the needful below
-
-		default:
-			// New minor release, do the usual processing
 		}
 
 		if rel.Prerelease && !upgradeToPreReleases {
+			l.Debugln("skipping pre-release", rel.Tag)
 			continue
 		}
 		for _, asset := range rel.Assets {
 			assetName := path.Base(asset.Name)
 			// Check for the architecture
 			expectedRelease := releaseName(rel.Tag)
-			l.Debugf("expected release asset %q", expectedRelease)
-			l.Debugln("considering release", assetName)
 			if strings.HasPrefix(assetName, expectedRelease) {
+				l.Debugln("selected", rel.Tag)
 				selected = rel
 			}
 		}