Create util method to check if email is empty

- Create method to check if email is empty or the default AuthMe email (avoids repetition)
- Check that input email has '@' inside text (relates to #1105)

src/main/java/fr/xephi/authme/command/executable/authme/debug/TestEmailSender.java

@@ -5,6 +5,7 @@ import fr.xephi.authme.datasource.DataSource;
 import fr.xephi.authme.datasource.DataSourceResult;
 import fr.xephi.authme.mail.SendMailSsl;
 import fr.xephi.authme.util.StringUtils;
+import fr.xephi.authme.util.Utils;
 import org.apache.commons.mail.EmailException;
 import org.apache.commons.mail.HtmlEmail;
 import org.bukkit.ChatColor;
@@ -69,7 +70,7 @@ class TestEmailSender implements DebugSection {
                 return null;
             }
             final String email = emailResult.getValue();
-            if (email == null || "your@email.com".equals(email)) {
+            if (Utils.isEmailEmpty(email)) {
                 sender.sendMessage(ChatColor.RED + "No email set for your account!"
                     + " Please use /authme debug mail <email>");
                 return null;

src/main/java/fr/xephi/authme/command/executable/email/RecoverEmailCommand.java

@@ -10,6 +10,7 @@ import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.service.CommonService;
 import fr.xephi.authme.service.PasswordRecoveryService;
 import fr.xephi.authme.service.RecoveryCodeService;
+import fr.xephi.authme.util.Utils;
 import org.bukkit.entity.Player;
 
 import javax.inject.Inject;
@@ -60,7 +61,7 @@ public class RecoverEmailCommand extends PlayerCommand {
         }
 
         final String email = emailResult.getValue();
-        if (email == null || !email.equalsIgnoreCase(playerMail) || "your@email.com".equalsIgnoreCase(email)) {
+        if (Utils.isEmailEmpty(email) || !email.equalsIgnoreCase(playerMail)) {
             commonService.send(player, MessageKey.INVALID_EMAIL);
             return;
         }

src/main/java/fr/xephi/authme/command/executable/email/ShowEmailCommand.java

@@ -5,6 +5,7 @@ import fr.xephi.authme.data.auth.PlayerAuth;
 import fr.xephi.authme.data.auth.PlayerCache;
 import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.service.CommonService;
+import fr.xephi.authme.util.Utils;
 import org.bukkit.entity.Player;
 
 import javax.inject.Inject;
@@ -24,7 +25,7 @@ public class ShowEmailCommand extends PlayerCommand {
     @Override
     public void runCommand(Player player, List<String> arguments) {
         PlayerAuth auth = playerCache.getAuth(player.getName());
-        if (auth != null && auth.getEmail() != null && !"your@email.com".equalsIgnoreCase(auth.getEmail())) {
+        if (auth != null && !Utils.isEmailEmpty(auth.getEmail())) {
             commonService.send(player, MessageKey.EMAIL_SHOW, auth.getEmail());
         } else {
             commonService.send(player, MessageKey.SHOW_NO_EMAIL);