Check block list host names

app/src/main/java/eu/faircode/email/DnsBlockList.java

@@ -25,6 +25,7 @@ import android.net.Uri;
 import android.text.TextUtils;
 
 import androidx.core.net.MailTo;
+import androidx.core.util.PatternsCompat;
 import androidx.preference.PreferenceManager;
 
 import java.net.Inet4Address;
@@ -165,6 +166,8 @@ public class DnsBlockList {
         boolean numeric = host.startsWith("[") && host.endsWith("]");
         if (numeric)
             host = host.substring(1, host.length() - 1);
+        else if (!PatternsCompat.DOMAIN_NAME.matcher(host).matches())
+            return null;
 
         return isJunk(context, host, true, BLOCK_LISTS);
     }