MM-31064: Simplify indentation (#16565)

* MM-31064: Simplify indentation

Reduce indentation where possible.

```release-note
NONE
```

Command ran to verify:
golangci-lint run --disable-all --enable golint --max-issues-per-linter=10000 --max-same-issues=100000 ./... | grep "block ends with a return state"

https://mattermost.atlassian.net/browse/MM-31064

* incorporate review comments

* enable golint for outdent rule

* fix remaining issues

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/preferences.go

@@ -19,9 +19,8 @@ func PreferencesFromJson(data io.Reader) (Preferences, error) {
 	decoder := json.NewDecoder(data)
 	var o Preferences
 	err := decoder.Decode(&o)
-	if err == nil {
-		return o, nil
-	} else {
+	if err != nil {
 		return nil, err
 	}
+	return o, nil
 }