Update SWCommandUtils SteamwarUser mapper

SpigotCore_Main/src/de/steamwar/sql/SteamwarUser.java

@@ -98,7 +98,7 @@ public class SteamwarUser {
 	}
 
 	public static List<SteamwarUser> getByPrefix(String userName){
-		if (userName.length() < 1) {
+		if (userName.isEmpty()) {
 			return new ArrayList<>();
 		}
 		List<SteamwarUser> users = byPrefix.get(userName.toLowerCase().substring(0, 1));