MM-31062: Rewrite empty string checks to be more idiomatic (#16587)

https://mattermost.atlassian.net/browse/MM-31062

```release-note
NONE
```

store/sqlstore/user_store.go

@@ -286,7 +286,7 @@ func (us SqlUserStore) UpdateAuthData(userId string, service string, authData *s
 			     AuthService = :AuthService,
 			     AuthData = :AuthData`
 
-	if len(email) != 0 {
+	if email != "" {
 		query += ", Email = lower(:Email)"
 	}