change images source in emails to base64

dmp-backend/web/src/main/java/eu/eudat/logic/services/utilities/MailServiceImpl.java

@@ -108,8 +108,11 @@ public class MailServiceImpl implements MailService {
             lastIndex = content.indexOf("img src=\"", lastIndex);
 
             if (lastIndex != -1) {
-                imagePaths.add(content.substring(lastIndex + 9, content.indexOf("\"", lastIndex + 9)));
-                lastIndex ++;
+                String imagePath = content.substring(lastIndex + 9, content.indexOf("\"", lastIndex + 9));
+                if (!imagePath.contains("data:image/png;base64")) {
+                    imagePaths.add(imagePath);
+                }
+                lastIndex++;
             }
         }