server: fix fail to list public ips of shared networks sometimes (#8624)

Author: weizhouapache

server/src/main/java/com/cloud/api/ApiResponseHelper.java

@@ -992,6 +992,12 @@ private void addSystemVmInfoToIpResponse(NicVO nic, IPAddressResponse ipResponse
         if (!isAdmin) {
             return;
         }
+        try {
+            nic.getInstanceId();
+        } catch (NullPointerException ex) {
+            return;
+        }
+
         VirtualMachine vm = ApiDBUtils.findVMInstanceById(nic.getInstanceId());
         if (vm == null) {
             return;