check if the provided ip address could be converted to an IPv4 address (eclipse#1627)

Author: netomi

server/src/main/java/org/eclipse/openvsx/ratelimit/CustomerService.java

@@ -54,6 +54,11 @@ public Optional<Customer> getCustomerById(long id) {
 
     public Optional<Customer> getCustomerByIpAddress(String ipAddress) {
         var ip = new IPAddressString(ipAddress).getAddress().toIPv4();
+        if (ip == null) {
+            logger.warn("Could not determine IP address from string {}", ipAddress);
+            return Optional.empty();
+        }
+        
         var node = customersByIPAddress.elementsContaining(ip);
         if (node != null) {
             return Optional.of(node.getValue());